Fixed a configuration problem for Sadic

Also changed the order of Python version checking.
Better Python support

 * Added a wrapper util header to handle const char* casting problems
   and strings
 * Fixed compilation for Python 2.x
 * Added HAVE_PYTHON inside config.h. Its value represent the python
   major version
Fixed forwarding arguments to PyObject_CallMethod

I completely forgot the problem about forwarding variadic arguments. It
was a long time I used... However, now the wrapper uses variadic
arguments.
Gromacs context created once per program
Should avoid locks on main thread

Yeah, I know that everything related to main thread-child threads
should need a complete rewrite...
Ok, a reference must be passed...