COMP: Python ExternalProject - Fix configure warnings, consistent symlinks

$ git shortlog 892c95b5..82e1494
Jean-Christophe Fillion-Robin (3):
      Merge branch '26-create-installed-python-executable-symlinks'
      Escape double-quote in ConfigureChecks to fix CMake 2.8.12.1 warnings.
      Merge branch '32-fix-cmake2.8.12.1-configure-warning'

Will Dicharry (1):
      Create versioned symlinks on install to match autoconf python install.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22831 3bd1e089-480b-0410-8dfb-8563597acbee