Correct wrong dependency of main package on the tk backend.

- Reinstantiate wx backend for python2.x.
- Run setup.py under xvfb-run to detect and default to gtk backend (#883502)
- Split qt4 backend subpackage and add proper requires for it.
- Correct wrong regex in tcl libdir patch.

python-matplotlib-tk.patch

@@ -8,7 +8,7 @@ diff -up matplotlib-1.2.0/setupext.py.orig matplotlib-1.2.0/setupext.py
 -                "/usr/lib/tcl"+str(Tkinter.TclVersion),
 -                "/usr/lib"]
 +                "@@libdir@@/tcl"+str(Tkinter.TclVersion),
-+                "@@lib@@"]
++                "@@libdir@@"]
      tk_poss = [tk_lib_dir,
                  os.path.normpath(os.path.join(tk_lib_dir, '..')),
 -               "/usr/lib/tk"+str(Tkinter.TkVersion),