This moves population and eviction of the "Persistence Cache" into WriteTransaction.

o Takes advantage of the fact that the exhaustive list of labels is known now, so replaces complex sorting/insert with simple replace.
o Does not address, but works around, the fact that labels are still longs in WriteTransaction. This needs to be addressed in a separate commit.
Merge pull request #1339 from jakewins/fix-cache-eviction

This moves population and eviction of the "Persistence Cache" into Write...