[POC] Backport TLS SNI support from Python 3.2

Here is a backport of the patch that added SNI support to Python 3.2, but for Python 2.X.

The upstream patch: http://hg.python.org/cpython/rev/846c0e1342d0/

Known issues:
- License compatibility for Python' s _ssl.c inclusion not checked
- Compiling of _ssl.c is not portable (just a handful of Unix-like paths)
- No test!

But it works with my SNI certificate, so I can use my own PyPI server through SSL now I switched to pip 1.3.