(#2655) - test and fix auto_compaction

Predictably, there were a few bugs in auto_compaction, but not as many as I thought.

This adds a Travis test for each of Node, Phantom, and Firefox to test auto-compaction. I hate adding this many tests to Travis, but I don't see any other way to do it, since the compaction logic is different for all three adapters, and I want to play it safe.
^ this happens when you compact an empty database