In addition, we're now switching to using refs/tags from git rather than commit
refs directly, which has the advantage, that we don't have to do bookkeeping
twice, where people forget to increment the version in nixpkgs.
This happened for the previous version, where `pkgver` had the value
"2011.12.08", but in rg3/youtube-dl@661a807c65 the
version actually is "2012.01.08b".
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
