Add OpenGL support

git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/gui/trunk@14997 72102866-910b-0410-8b05-ffd578937521

Source/GSDisplayServer.m

@@ -245,6 +245,17 @@ GSCurrentServer(void)
   [super dealloc];
 }
 
+- glContextClass
+{
+  return nil;
+}
+
+- glPixelFormatClass
+{
+  return nil;
+}
+
+
 /* Drag and drop support. */
 /** Convienience method that calls -addDragTypes:toWindow: using the
     server that controls win.