COMP: Update build-system to use CMake'ified python

Latest stable version 2.7.3 is now used instead of ancient 2.6.6

Directory layout has been updated:
 - Python-2.7.3   : source
 - python         : build system
 - python-build   : build tree
 - python-install : install tree

Associated external project has been simplified. Removed unneeded
custom configure, make and install steps. Also removed unneeded
patch steps.

Note that the pythonrun.h and pythonrun.c are still patched in order
to prevent crash (related to dll boundaries [1][2]) when building Slicer debug
against a released python.

[1] http://stackoverflow.com/questions/2322095/why-does-this-program-crash-passing-of-stdstring-between-dlls
[2] http://social.msdn.microsoft.com/Forums/en-US/vcgeneral/thread/57e0d522-a42c-4add-963d-c87c6e76f161