Add cil keywords to string pool.

Since we are comparing strings that are in the string pool
to CIL_KEY_*, we can add all of the CIL_KEY_* to the string pool.
We can then do reference comparisons for string equality rather than
strcmp for increased performance.

This patch has an overall performance gain of ~4%.

Signed-off-by: Yuli Khodorkovskiy <ykhodorkovskiy@tresys.com>
Signed-off-by: James Carter <jwcart2@tycho.nsa.gov>
Create CIL keywords for "object_r" and "*".

Eliminated some additional strcmp calls.

Signed-off-by: James Carter <jwcart2@tycho.nsa.gov>