Partially (re-?)unified some of the glutMainLoopEvent() code. The only

Partially (re-?)unified some of the glutMainLoopEvent() code.  The only
code that really needs to be system-specific is the window event handling,
which in MS-WINDOWS is tucked into a separate function.  In UNIX/X11, it's
all spilled out into glutMainLoopEvent() for some reason.

If the X11 code could be tucked into another function, glutMainLoopEvent()
could be platform-independant.

git-svn-id: svn+ssh://svn.code.sf.net/p/freeglut/code/trunk/freeglut/freeglut@245 7f0cb862-5218-0410-a997-914c9d46530a