Even though this was an X11-specific hack, interest has been
shown to have it re-added to PDL. This ticket is to remind
and track any issues with this process.
NOTE: The current status is that non-X11 Tk doesn't have
support for embedded OpenGL context in widgets so
this would not be cross-platform portable to other OSes
not using X11 (such as the native MacOS X or win32).