vbo: return VP_NONE from get_program_mode() if running fixed-func vertex program
vbo: return VP_NONE from get_program_mode() if running fixed-func vertex program

If we're running a vertex program to emulated fixed-function, we still need
to treat vertex arrays/attributes as if we're in fixed-function mode.

This should probably be back-ported to Mesa 7.5 after a bit more testing.

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