I've had the ensuing patches on my tree for a few days. A quick outline of what
1) Replace the old libfetch method of setting useragent (via an environment
var) with proper get/set methods.
2) Refactor signature downloading to ensure that the sig file is downloaded
from the same mirror as the file itself.
3) Add handling for VerifySig in the [options] section of pacman.conf. This
should probably be split into two patches (front end/back end), as it adds
another API interface. I'm not sold on the naming convention I've used either.