Snapshots are not preserved across compaction

[rnarubin]

see here as it differs from here

I have some unit tests that demonstrate this failing (so it's not just speculation on the source). If no one picks this up i'll probably fix it eventually

[rnarubin]

This turns out to be a bigger problem than anticipated, whole versions were being preserved in the place of snapshots. Anyone relying on maintaining many snapshots would be using a great deal of resources needlessly. Working on fixing this.