Document why Mesa is stuck at an older version

git-svn-id: https://rebeccablackos.svn.sourceforge.net/svnroot/rebeccablackos@3279 56e3d1a8-0179-4092-b3e2-9fbbcda0c0a9
Install now missing gnome-shell dependancies

git-svn-id: https://rebeccablackos.svn.sourceforge.net/svnroot/rebeccablackos@3280 56e3d1a8-0179-4092-b3e2-9fbbcda0c0a9
Remove comented-out builders that are not needed

git-svn-id: https://rebeccablackos.svn.sourceforge.net/svnroot/rebeccablackos@3281 56e3d1a8-0179-4092-b3e2-9fbbcda0c0a9
document new control file

git-svn-id: https://rebeccablackos.svn.sourceforge.net/svnroot/rebeccablackos@3282 56e3d1a8-0179-4092-b3e2-9fbbcda0c0a9