Finally fix OSX bug reported by Michail Vidiassov:  use windowWillClose, not dealloc, to deallocate rgl stuff.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rgl@1123 79a1b648-8b68-254f-b20b-c0b50f5137bf
Clean up switch from dealloc to windowWillClose

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rgl@1124 79a1b648-8b68-254f-b20b-c0b50f5137bf