GL: Ensure mesa_devel and mesa_swrast are always present

* As the OpenGL kit is assumed by most ports (and BeOS apps)
  to "exist", lets make mesa_devel present by default until
  post R1
* mesa_swrast ensures we always have the basic swrast renderer
  To play with mesa_swpipe (gallium llvmpipe, gcc4) uninstall
  mesa_swrast and install mesa_swpipe. (you can install both,
  but it's first renderer found, first used atm)