Fix unpickling POSError subclasses under PyPy. This fixes a bunch of...

Fix unpickling POSError subclasses under PyPy. This fixes a bunch of '<Unprintable POSKeyError>' tests in ZEO.

src/ZODB/DB.py

@@ -561,7 +561,7 @@ class DB(object):
                 # and we also want to pretend that doesn't exist.
                 # If we have no way to get a refcount, we return False to symbolize
                 # that. As opposed to None, this has the advantage of being usable
-                # as a number (0) in case clients depended on that
+                # as a number (0) in case clients depended on that.
                 detail.append({
                     'conn_no': cn,
                     'oid': oid,

src/ZODB/POSException.py

@@ -61,6 +61,16 @@ class POSError(Exception):
 
             return (_recon, (self.__class__, state))
 
+        def __setstate__(self, state):
+            # PyPy doesn't store the 'args' attribute in an instance's
+            # __dict__; instead, it uses what amounts to a slot. Because
+            # we customize the pickled representation to just be a dictionary,
+            # the args would then get lost, leading to unprintable exceptions
+            # and worse. Manually assign to args from the state to be sure
+            # this doesn't happen.
+            super(POSError,self).__setstate__(state)
+            self.args = state['args']
+
 class POSKeyError(POSError, KeyError):
     """Key not found in database."""