add the same conditional mangling stuff that gl.h has.

include/GL/glu.h

@@ -30,6 +30,10 @@
 #ifndef __glu_h__
 #define __glu_h__
 
+#if defined(USE_MGL_NAMESPACE)
+#include "glu_mangle.h"
+#endif
+
 #include <GL/gl.h>
 
 #ifdef __cplusplus