Merge r3079:3080 from branches/SDL-1.2: disable glX if no glu.h header.

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%402359

configure.in

@@ -1374,6 +1374,7 @@ CheckOpenGLX11()
         AC_TRY_COMPILE([
          #include <GL/gl.h>
          #include <GL/glx.h>
+         #include <GL/glu.h>
         ],[
         ],[
         video_opengl=yes