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 reviewed:
 - Python-2.7.3   : source
 - python         : build system
 - python-build   : build tree
 - python-install : install tree

Associated external project has been simplified. Removed now 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

Anticipating the possibility to build Slicer against a system python,
introduced variable HAVE_PYRUN_CLOSEFILE and HAVE_PYRUN_OPENFILE variable
to be able to conditionally build Slicer library with fopen/fclose
built-in the python library.