[plt-scheme] avoiding GLX warnings

When I make a canvas% on a VNC X display, I get these warnings:

MrEd version 299.101, Copyright (c) 2004-2005 PLT Scheme, Inc.
> (define frame (instantiate frame% ("foo")))
> (define canvas (instantiate canvas% (frame)))
Xlib:  extension "GLX" missing on display ":1.0".
Xlib:  extension "GLX" missing on display ":1.0".
Xlib:  extension "GLX" missing on display ":1.0".
>

I guess the VNC X server doesn't have a GLX emulator.  Is there a way
to avoid these warnings?

--dougo at place.org