(Merge 3.2) Issue #9756: When calling a method descriptor or a slot wrapper

descriptor, the check of the object type doesn't read the __class__ attribute
anymore.  Fix a crash if a class override its __class__ attribute (e.g. a proxy
of the str type).

diff --cc Lib/test/test_descr.py
Simple merge

diff --cc Misc/NEWS
index 1e31c8f9d69efeb553a780922a33b858c16b741f,381c7f27a6bb61e282805ea07d8651c1accc1e5b..d9af0c4f6d9baf7561ade7cc98f563e865dfd42a
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -10,10 -10,11 +10,15 @@@ What's New in Python 3.3 Alpha 1
  Core and Builtins
  -----------------
  
+ - Issue #9756: When calling a method descriptor or a slot wrapper descriptor,
+   the check of the object type doesn't read the __class__ attribute anymore.
+   Fix a crash if a class override its __class__ attribute (e.g. a proxy of the
+   str type).
+ 
 +- Issue #10517: After fork(), reinitialize the TLS used by the PyGILState_*
 +  APIs, to avoid a crash with the pthread implementation in RHEL 5.  Patch
 +  by Charles-François Natali.
 +
  - Issue #10914: Initialize correctly the filesystem codec when creating a new
    subinterpreter to fix a bootstrap issue with codecs implemented in Python, as
    the ISO-8859-15 codec.