Make sure to check for glu.h before enabling glX support. We don't
directly need GLU, but SDL_opengl.h tries to include it, and it shows that
the workstation is misconfigured or incompletely configured if just this
one header is missing.
Fixes Bugzilla #336.
--- a/configure.in Fri Jun 15 11:43:14 2007 +0000
+++ b/configure.in Fri Jun 15 12:26:29 2007 +0000
@@ -1550,6 +1550,7 @@
AC_TRY_COMPILE([
#include <GL/gl.h>
#include <GL/glx.h>
+ #include <GL/glu.h>
],[
],[
video_opengl=yes