mesa: make ARB_debug_output functions an alias of

mesa: make ARB_debug_output functions an alias of
 KHR_debug

Also update dispatch sanity removing ARB_debug_output checks and
removing KHR_debug placeholders as the checks have already been added

V2: Make sure we exit case statements with conditional breaks rather than
just dropping through.

Signed-off-by: Timothy Arceri <t_arceri@yahoo.com.au>
Reviewed-by: Brian Paul <brianp@vmware.com>