setlocalversion: update mercurial tag parsing

The tag output of hg doesn't quite match what setlocalversion currently
expects, so update it to handle the latest format.

Signed-off-by: Mike Crowe <mcrowe@zipitwireless.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>