openglcontrol: gtk2: using colormap needed for multisampling

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@40438 4005530d-fff6-0310-9dd1-cebe43e6787f
openglcontrol: clean up

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@40439 4005530d-fff6-0310-9dd1-cebe43e6787f