[PATCH] Fix GLXEXT typo

This one just keeps coming back to bite me... fix a typo in my attempt
to get glXGetProcAddressARB defined (GXEXT -> GLXEXT).

diff -urN a/common/gl_vidlinuxglx.c head/common/gl_vidlinuxglx.c
--- a/common/gl_vidlinuxglx.c	2006-02-18 11:34:50.000000000 +1030
+++ head/common/gl_vidlinuxglx.c	2006-02-19 08:43:24.000000000 +1030
@@ -26,7 +26,7 @@
 #include <stdio.h>
 #include <signal.h>
 
-#define GLX_GLEXT_PROTOTYPES
+#define GLX_GLXEXT_PROTOTYPES
 #include <GL/glx.h>
 
 #include <X11/keysym.h>