Enable faster regex searching and fix pool counter

Now that we've built the ngram index for regexes we can use it!

We fix the pool counter two ways:
1.  Raise the number of concurrent regex searches.  They are lower overhead
when using trigrams so we can support more of them.
2.  Add pool counter for namespaces lookups.  Cirrus now supports this so
we ought to have a pool counter for it.

Change-Id: Ia82c8113534879a27ed0fea83a667dc625bd459b