This fixes the problem where 0.4.12-dev versions were erroneously shown as
0.4.11-dev because the tag was added on a separate branch. It also fixes a
similar issue when builders didn't fetch new tags when updating.
This also removes the number-of-commits-since-tag field, since it's
incompatible with this. Said field doesn't seem to be useful anyway if you
have the commit hash.
1be2d32fd5