fix some bugs related to compact()

Hey, just a heads up - I do not know what I'm doing here...
But the changes that I've added made the failing test cases work.

This is just a first commit, I'll take a closer look later to see if the changes I've done got some sideeffects. And get some more tests written.
without this, after doing one compaction and then doing another, I end up trying reading files that don't exists anymore.