Clean up handling of RollbackException so that other stores can do similar things

Move it out of Postgres server and into PersistitAdapter. Make every place that handled PersistitException also handle RollbackException. Since RollbackException is a RuntimeException, it isn't certain that this is every place that was getting it before, but it seems likely.

Change names and inheritance of exceptions to make it more like other adapter exceptions and less like timeout and cancel.