Merge from 3.4.

Issue #21435: Segfault in gc with cyclic trash
Changed the iteration logic in finalize_garbage() to tolerate objects vanishing
from the list as a side effect of executing a finalizer.

diff --cc Misc/NEWS
index 6fc0a13dc6ee64efddca36eb21aafa445cad761a,d0d9012ffbaf87d13217720ebba3126ccf5a2de4..04bf8545b9be857048de8f5103e8295269419709
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -10,17 -10,29 +10,21 @@@ Release date: TB
  Core and Builtins
  -----------------
  
 -Library
 --------
 -
 -- Issue #21396: Fix TextIOWrapper(..., write_through=True) to not force a
 -  flush() on the underlying binary stream.  Patch by akira.
 -
 -Tests
 ------
+ - Issue #21435: In rare cases, when running finalizers on objects in cyclic
+   trash a bad pointer dereference could occur due to a subtle flaw in
+   internal iteration logic.
+ 
 +- Issue #21233: Add new C functions: PyMem_RawCalloc(), PyMem_Calloc(),
 +  PyObject_Calloc(), _PyObject_GC_Calloc(). bytes(int) and bytearray(int)
 +  are now using ``calloc()`` instead of ``malloc()`` for large objects which
 +  is faster and use less memory (until the bytearray buffer is filled with
 +  data).
  
 -- Issue #17752: Fix distutils tests when run from the installed location.
 -
 -
 -What's New in Python 3.4.1rc1?
 -==============================
 -
 -Release date: 2014-05-05
 +- Issue #21377: PyBytes_Concat() now tries to concatenate in-place when the
 +  first argument has a reference count of 1.  Patch by Nikolaus Rath.
  
 -Core and Builtins
 ------------------
 +- Issue #20355: -W command line options now have higher priority than the
 +  PYTHONWARNINGS environment variable.  Patch by Arfrever.
  
  - Issue #21274: Define PATH_MAX for GNU/Hurd in Python/pythonrun.c.
  

diff --cc Modules/gcmodule.c
Simple merge