PySide compatibility with stackless

This is a minimal patch that makes compilation of PySide work with
stackless python. It is needed in conjunction with my pull request on
the pyside repo.

The problem was the different layout of frames in stackless, where the
field "ht_type" does not exist. Instead, stackless always uses the extended type,
and all fields are accessible without "ht_type".

I introduced a few macros which put these differences into a central place:
sbkpython.h
and made sure that this file is included also in all generated files.

Tested to build correctly on OS X with

stackless on python 2.7.5
plain python 2.7.5
plain python 3.3

This patch does not need to be touched again.

Cheers - Chris