program: Allow redundant OPTION ARB_fog_* directives.

program: Allow redundant OPTION ARB_fog_* directives.

A fragment program from "Pixel Piracy" contains redundant OPTION
directives:

!!ARBfp1.0
OPTION ARB_precision_hint_fastest;
OPTION ARB_fog_exp2;
OPTION ARB_precision_hint_fastest;
OPTION ARB_fog_exp2;
...

We already allow redundant ARB_precision_hint_fastest directives, but
disallow the redundant (yet consistent) ARB_fog_exp2 directives, failing
to compile the program.

The specification seems to contradict itself - the main text says that
only one fog application option may be specified, but then backpedals,
indicating the intent is to disallow /contradictory/ flags.  One of the
issues suggests that specifying contradictory ones is stupid, but
allowed, and only the last one should take effect.

Accepting multiple redundant (but consistent) directives seems harmless,
and like a reasonable interpretation of the specification.  It also
fixes a fragment program found in the wild.

Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>