Simplify and robustify the python library and include detection (use

the actuall python used to get info on the paths).

In root-config add new options:
--python-version     Print the Python version used by ROOT
--svn-revision       Print the ROOT SVN revision number


git-svn-id: http://root.cern.ch/svn/root/trunk@20303 27541ba8-7e3a-0410-8455-c3a389f83636