Merge r71222 from old branch:

  Allow assignment to a wrapper's __parent__.

_Acquisition.c

@@ -627,8 +627,8 @@ Wrapper_setattro(Wrapper *self, PyObject *oname, PyObject *v)
 
   /* Allow assignment to parent, to change context. */
   if (PyString_Check(oname)) name=PyString_AS_STRING(oname);
-  if (*name=='a' && name[1]=='q' && name[2]=='_' 
-      && strcmp(name+3,"parent")==0)
+  if ((*name=='a' && name[1]=='q' && name[2]=='_' 
+       && strcmp(name+3,"parent")==0) || (strcmp(name, "__parent__")==0))
     {
       Py_XINCREF(v);
       ASSIGN(self->container, v);

tests.py

@@ -1401,14 +1401,28 @@ def test_creating_wrappers_directly():
     ...
     TypeError: __init__() takes exactly 2 arguments (1 given)
 
-    We can reassign aq_parent
+    We can reassign aq_parent / __parent__ on a wrapper:
 
     >>> x = B()
     >>> x.color = 'green'
     >>> w.aq_parent = x
     >>> w.color
     'green'
 
+    >>> y = B()
+    >>> y.color = 'blue'
+    >>> w.__parent__ = y
+    >>> w.color
+    'blue'
+
+    Note that messing with the wrapper won't in any way affect the
+    wrapped object:
+
+    >>> Acquisition.aq_base(w).__parent__
+    Traceback (most recent call last):
+    ...
+    AttributeError: __parent__
+
     >>> w = ImplicitAcquisitionWrapper()
     Traceback (most recent call last):
     ...