name-rev: refactor logic to see if a new candidate is a better name

name-rev: refactor logic to see if a new candidate is a better name

When we encounter a new ref that could describe the commit we are
looking at, we compare the name that is formed using that ref and
the name we found so far and pick a better one.

Factor the comparison logic out to a separate helper function, while
keeping the current logic the same (i.e. a name that is based on an
older tag is better, and if two tags of the same age can reach the
commit, the one with fewer number of hops to reach the commit is
better).

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Michael J Gruber <git@grubix.eu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>