Make zope.proxy and persistent direct dependencies since we import from them,...

Make zope.proxy and persistent direct dependencies since we import from them, and pin them to the versions we need for pure-python operation.

setup.py

@@ -73,6 +73,8 @@ install_requires = [
     'zope.size',
     'zope.traversing>=4.0.0a1',
     'zope.publisher',
+    'zope.proxy>=4.1.5',
+    'persistent>=4.1.0',
     'BTrees'
 ]
 if not is_pypy: