lang/python{31,32,33}: Add clang 3.4 fix from python27

Copy change committed to python27 [1] to python31, python32 and
python33 to fix builds of some extensions with Clang 3.4.

Also add breadcrumbs to the patch header in lang/python27 referencing
the upstream issue. [2]

The Python 3.4 port (lang/python34) already carries the patch.

[1] https://svnweb.freebsd.org/ports?view=revision&revision=346428
[2] http://bugs.python.org/issue20767