should still be customized by the user; add UID check; fix bug with
non-existent repo directories (thanks to Mauro for the even less buggy fix);
fix bug with a subshell that prevented sspm from exiting on one error - it was
meant to be a group command; convert the su block into a normal block; add a
couple more exclusions to the tar command to skip backup and tags files - and
throw a note into the ChangeLog so users don't get surprised by the repo
moving or having its ownership changed
