#5 Need an open window before calling "glutGet"

[John F. Fay]

In the "comp.c" demo in the "advanced" directory, we
find that we need a window to be defined before
"glutGet ( GLUT_DISPLAY_MODE_POSSIBLE )" can be
called. GLUT does not have this restriction. In
"freeglut" there is a check at the beginning of the
"fgSetupPixelFormat" call and a few references to
"window->" later in the function.