#11 Menus can't have multiple parents.

[Richard Rauch]

A long-standing bug with freeglut/OpenGLUT is the
inability to bind a menu to multiple parents. The
attempt will result in display bugs and possibly
crashes.

This is a serious incompatibility with GLUT, so freeglut
needs to fix this desperately.

For OpenGLUT, this should be fixed because it is just
obviously wrong and crashes the application the way that
the OpenGLUT code works.

For OpenGLEAN, the problem will likely be finessed by
just removing the menu system from OpenGLEAN. Still,
a bug is a bug is a bug.

(Incidental: freeglut has put some work into addressing
this. It's not clear if they have truly fixed the bug,
or only partially fixed it, or maybe not truly done
anything for it.)

This corresponds to OpenGLUT bug: 947231