Modified the string pool so that all strings are destroyed at the end
from the string pool.

Keeping the strings around does not cost much memory and eliminates the
need for reference counting and a large number of hashtable operations.

This results in ~10% faster policy creation times.

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