Use a bit more POSIX compatible commands.
Fix locking to work on Linux too: use locks/ lockdir.
Use current user's ssh_known file, don't dig it up from passwd according
to the user in the backup job.
Unbreak locate db creation.
Remove a couple of stray lines from old code. Fix expiration and don't
use local foo=assignment but local foo; foo=assignment.
A more safe way to match snapshot directories is to account for
slash / at the end of the output too.
Improved removal of old snapshots, allow to define:

- time interval in days
- minimum and maximum parameters for that interval

Old configuration is incompatible with this commit, please update.