Mount snapshots in daterange and ancillary changes

In my testing I noticed only the most recent snapshot was ever mounting, so I added a date range flag and changed the code to explicitly test if the dates in snapcollection were in that range, rather than greping each item for a date matching a pattern.

I also changed the code releating to checking if snaps were already mounted to use mount instead of ls. I've had to do a hard reboot once or twice and the existing code would get confused, thinking the snapshots were still mounted (when in fact they weren't). Finally, I added code to cleanup mountpoints in case this happens.