fixes two cases of menu's not closing when they should:

fixes two cases of menu's not closing when they should:
1. open a menu in one of the freeglut windows, then activate another app
(or the console window) by clicking on that. The freeglut menu doesn't
close, and as it is topmost, it shines through everything.
2. open a menu in one of the freeglut windows, then click on the
non-client area of another freeglut window (e.g. the title bar): menu
doesn't close

git-svn-id: svn+ssh://svn.code.sf.net/p/freeglut/code/trunk/freeglut/freeglut@1352 7f0cb862-5218-0410-a997-914c9d46530a