Fixing bug 3292122 from Nigel Stewart (thanks, Nigel) so that "freeglut" will build...

Fixing bug 3292122 from Nigel Stewart (thanks, Nigel) so that "freeglut" will build on Ubuntu, per e-mail from Diederick Niehorster vintage 6/8/2011 at 3:07 AM.  There was a problem with variables being declared only with an X extension but being used for all of X.

git-svn-id: svn+ssh://svn.code.sf.net/p/freeglut/code/trunk/freeglut/freeglut@927 7f0cb862-5218-0410-a997-914c9d46530a