be more careful about closing menus when focus changes. Only do so when new focus...

Also simplified situation in which menus are SW_SHOWed... if a gamemode window is open, it must the parent of any active windows as there can be no other windows open on top of the gamemode window.

git-svn-id: svn+ssh://svn.code.sf.net/p/freeglut/code/trunk/freeglut/freeglut@1716 7f0cb862-5218-0410-a997-914c9d46530a