Now git-annex's self-upgrade code will check the gpg signature of a
new version before using it.

To do this I had to include the gpg public keys into the
git-annex distribution, and that raised the question of which public keys
to include. Currently I have both the dedicated git-annex distribution
signing key, and my own gpg key as a backup in case I somehow misplace the
former.

Also spent a while looking at the recent logs on the web server. There
seem to be around 600 users of the assistant with
upgrade checking enabled. That breaks down to 68% Linux amd64, 20% Linux
i386, 11% OSX Mavericks, and 0.5% OSX Lion.

Most are upgrading successfully, but there are a few that seem to
repeatedly fail for some reason. (Not counting the OSX Lion, which will
probably never find an upgrade available.) I hope that someone who is
experiencing an upgrade failure gets in touch with some debug logs.

In the same time period, around 450 unique hosts manually downloaded a
git-anex distribution. Also compare with Debian popcon, which has 1200
reporting git-annex users.
