Fix for bug #8132: on Mac OS X 10.5 with Nvidia cards drawing

background images and node previews goes wrong. The exact cause
of that is not sure, may be a driver bug, workaround is to fall
back to another slower function.

source/blender/include/BIF_glutil.h

@@ -204,6 +204,7 @@ void bglVertex2fv(float *vec);
 /* intel gfx cards frontbuffer problem */
 void bglFlush(void);
 int is_a_really_crappy_intel_card(void);
+int is_a_really_crappy_nvidia_card(void);
 void set_inverted_drawing(int enable);