Phoenix 180

First revision for review.  There are some open points here.  Still no test case added to consume the stats.  Will do the performance test once the system is available with me.
Rather than have a separate cache for this, I'd rather piggyback on the existing cache. How about if we just read the stats anytime we re-load the PTable? Then an updateStats would just need to invalidate the cache entry for the table. Next time the table is accessed, the stats table would be re-read.

One side note: we'll want to make sure that the PStats info has a getEstimatedByteSize() and that PTable takes this into account for it's getEstimatedByteSize() so that this is accounted for in the size of each cached PTable.