HAMMER - Add additional warnings for v2/v3 upgrades, fix bug in snaprm
* Add warnings related to backup scripts when upgrading from V2 to V3.
The synctid directive does not generate a snapshot. You should generate
a real snapshot to properly track them.
Also, removing a snapshot softlink does not remove the meta-data and
thus the pruning code will continue to prune around that snapshot.
The snaprm directive should be used when removing snapshot softlinks
to also remove the meta-data.
* Snaprm now uses the current directory when removing a transaction id
and no target directory was specified.
* Snaprm now makes it clear that a failure to remove meta-data when
removing a softlink is just a warning, not a fatal error.