[GtkGLExt] Problems starting gtk_gl_init

[John Coppens <john jcoppens com>]

Hello all...

I just converted a program of mine from gtkglarea to gtkglext, and find that I cannot
even call gtk_gl_init... I see this error:

(process:21187): Gdk-CRITICAL **: IA__gdk_x11_display_get_xdisplay: assertion `GDK_IS_DISPLAY (display)' 
failed

The gtk_gl_init call is at the start of the program.

The program worked fine with with gtkglarea, but I needed the glAccum 
functionality and didn't find any reference to that in gtkglarea.
Tracing a little with gdb showed an error with glx - but I don't
understand where that comes from. glxgears/glxinfo all work ok.

John