ZODB Components: Fix deadlock between import lock and aq_method_lock.

This only happens when using ZEO (see source code comments).

Steps to reproduce:
  1. Edit a ZODB Component in one tab.
  2. At the same time, run Unit Tests in another tab.

Backtrace:

  # ThreadID: 140153540167424
  File: "eggs/Zope2-2.13.22-py2.7.egg/ZServer/PubCore/ZServerPublisher.py", line 31, in __init__
    response=b)
  File: "eggs/Zope2-2.13.22-py2.7.egg/ZPublisher/Publish.py", line 455, in publish_module
    environ, debug, request, response)
  File: "eggs/Zope2-2.13.22-py2.7.egg/ZPublisher/Publish.py", line 249, in publish_module_standard
    response = publish(request, module_name, after_list, debug=debug)
  File: "parts/erp5/Products/Localizer/patches.py", line 84, in new_publish
    x = zope_publish(request, module_name, after_list, debug)
  File: "eggs/Zope2-2.13.22-py2.7.egg/ZPublisher/Publish.py", line 138, in publish
    request, bind=1)
  File: "eggs/Zope2-2.13.22-py2.7.egg/ZPublisher/mapply.py", line 44, in mapply
    f, count = zope.publisher.publish.unwrapMethod(object)
  File: "eggs/zope.publisher-3.12.6-py2.7.egg/zope/publisher/publish.py", line 46, in unwrapMethod
    elif getattr(unwrapped, 'func_code', None) is not None:
  File: "eggs/Products.ExternalMethod-2.13.0-py2.7.egg/Products/ExternalMethod/ExternalMethod.py", line 106, in <lambda>
    func_code = ComputedAttribute(lambda self: self.getFuncCode())
  File: "eggs/Products.ExternalMethod-2.13.0-py2.7.egg/Products/ExternalMethod/ExternalMethod.py", line 190, in getFuncCode
    self._v_f = self.getFunction()
  File: "parts/erp5/Products/ERP5Type/patches/ExternalMethod.py", line 29, in getFunction
    level=0)
  File: "parts/erp5/Products/ERP5Type/dynamic/component_package.py", line 407, in load_module
    with aq_method_lock:
  File: "parts/python2.7/lib/python2.7/threading.py", line 174, in acquire
    rc = self.__block.acquire(blocking)

  => 1. Acquire Import lock in getFunction() (ZODB Component import)
     2. Try to acquire aq_method_lock

  # ThreadID: 140153468495616
  File: "eggs/Zope2-2.13.22-py2.7.egg/ZServer/PubCore/ZServerPublisher.py", line 31, in __init__
    response=b)
  File: "eggs/Zope2-2.13.22-py2.7.egg/ZPublisher/Publish.py", line 455, in publish_module
    environ, debug, request, response)
  File: "eggs/Zope2-2.13.22-py2.7.egg/ZPublisher/Publish.py", line 249, in publish_module_standard
    response = publish(request, module_name, after_list, debug=debug)
  File: "parts/erp5/Products/Localizer/patches.py", line 84, in new_publish
    x = zope_publish(request, module_name, after_list, debug)
  File: "eggs/Zope2-2.13.22-py2.7.egg/ZPublisher/Publish.py", line 138, in publish
    request, bind=1)
  File: "eggs/Zope2-2.13.22-py2.7.egg/ZPublisher/mapply.py", line 77, in mapply
    if debug is not None: return debug(object,args,context)
  File: "eggs/Zope2-2.13.22-py2.7.egg/ZPublisher/Publish.py", line 48, in call_object
    result=apply(object,args) # Type s<cr> to step into published object.
  File: "parts/erp5/Products/TimerService/TimerService.py", line 90, in process_timer
    subscriptions.append(self.unrestrictedTraverse(path))
  File: "eggs/Zope2-2.13.22-py2.7.egg/OFS/Traversable.py", line 249, in unrestrictedTraverse
    if getattr(aq_base(obj), name, _marker) is not _marker:
  File: "parts/erp5/Products/ERP5Type/dynamic/lazy_class.py", line 107, in __getattribute__
    self.__class__.loadClass()
  File: "parts/erp5/Products/ERP5Type/dynamic/lazy_class.py", line 326, in loadClass
    class_definition = generatePortalTypeClass(site, portal_type)
  File: "parts/erp5/Products/ERP5Type/dynamic/portal_type_class.py", line 143, in generatePortalTypeClass
    type_class = portal_type.getTypeClass()
  File: "eggs/ZODB3-3.10.5+slapospatched001-py2.7-linux-x86_64.egg/ZODB/Connection.py", line 860, in setstate
    self._setstate(obj)
  File: "eggs/ZODB3-3.10.5+slapospatched001-py2.7-linux-x86_64.egg/ZODB/Connection.py", line 914, in _setstate
    self._reader.setGhostState(obj, p)
  File: "eggs/ZODB3-3.10.5+slapospatched001-py2.7-linux-x86_64.egg/ZODB/serialize.py", line 612, in setGhostState
    state = self.getState(pickle)
  File: "eggs/ZODB3-3.10.5+slapospatched001-py2.7-linux-x86_64.egg/ZODB/serialize.py", line 604, in getState
    unpickler.load() # skip the class metadata
  File: "eggs/ZODB3-3.10.5+slapospatched001-py2.7-linux-x86_64.egg/ZODB/serialize.py", line 474, in find_global
    return factory(conn, modulename, name)
  File: "eggs/Zope2-2.13.22-py2.7.egg/Zope2/App/ClassFactory.py", line 21, in ClassFactory
    m=__import__(module, _globals, _globals, _silly)

  => 1. Acquire aq_method_lock (generatePortalTypeClass())
     2. Try to import module and acquire Import lock

product/ERP5Type/dynamic/component_package.py

@@ -241,25 +241,6 @@ class ComponentDynamicPackage(ModuleType):
     As per PEP-302, raise an ImportError if the Loader could not load the
     module for any reason...
     """
-    # In Python < 3.3, the import lock is a global lock for all modules:
-    # http://bugs.python.org/issue9260
-    #
-    # So, release the import lock acquired by import statement on all hooks to
-    # load objects from ZODB. When an object is requested from ZEO, it sends a
-    # RPC request and lets the asyncore thread gets the reply. This reply may
-    # be a tuple (PICKLE, TID), sent directly to the first thread, or an
-    # Exception, which tries to import a ZODB module and thus creates a
-    # deadlock because of the global import lock
-    #
-    # Also, handle the case where find_module() may be called without import
-    # statement as it does change anything in sys.modules
-    import_lock_held = True
-    try:
-      imp.release_lock()
-    except RuntimeError:
-      import_lock_held = False
-
-    try:
     site = getSite()
     name = fullname[len(self._namespace_prefix):]
 
@@ -327,15 +308,8 @@ class ComponentDynamicPackage(ModuleType):
     source_code_str = component.getTextContent(validated_only=True)
     version_package = self._getVersionPackage(version)
 
-    finally:
-      # Internal release of import lock at the end of import machinery will
-      # fail if the hook is not acquired
-      if import_lock_held:
-        imp.acquire_lock()
-
     # All the required objects have been loaded, acquire import lock to modify
     # sys.modules and execute PEP302 requisites
-    if not import_lock_held:
     imp.acquire_lock()
     try:
       # The module *must* be in sys.modules before executing the code in case
@@ -393,10 +367,6 @@ class ComponentDynamicPackage(ModuleType):
 
       return module
     finally:
-      # load_module() can be called outside of import machinery, for example
-      # to check first if the module can be handled by Component and then try
-      # to load it without going through the same code again
-      if not import_lock_held:
       imp.release_lock()
 
   def load_module(self, fullname):
@@ -404,8 +374,34 @@ class ComponentDynamicPackage(ModuleType):
     Make sure that loading module is thread-safe using aq_method_lock to make
     sure that modules do not disappear because of an ongoing reset
     """
-    with aq_method_lock:
+    # In Python < 3.3, the import lock is a global lock for all modules:
+    # http://bugs.python.org/issue9260
+    #
+    # So, release the import lock acquired by import statement on all hooks to
+    # load objects from ZODB. When an object is requested from ZEO, it sends a
+    # RPC request and lets the asyncore thread gets the reply. This reply may
+    # be a tuple (PICKLE, TID), sent directly to the first thread, or an
+    # Exception, which tries to import a ZODB module and thus creates a
+    # deadlock because of the global import lock
+    #
+    # Also, handle the case where find_module() may be called without import
+    # statement as it does not change anything in sys.modules
+    import_lock_held = True
+    try:
+      imp.release_lock()
+    except RuntimeError:
+      import_lock_held = False
+
+    aq_method_lock.acquire()
+    try:
       return self.__load_module(fullname)
+    finally:
+      aq_method_lock.release()
+
+      # Internal release of import lock at the end of import machinery will
+      # fail if the hook is not acquired
+      if import_lock_held:
+        imp.acquire_lock()
 
   def find_load_module(self, name):
     """