I cannot see upper side of a long menu (i.e. a menu
with many items) when its height is taller than half of
Of course, the menu taller than the screen cannot be in
sight . I'd like to use half to full sized menu.
Patch for this feature is attached.
This patch lowers the menu to the position where we can
see the first item.
freeglut has a larger menu font than GLUT 3.7, so I
took such situations much more serious.