Test updates and related bug fixes

I just set up some big tests of generating repos based on feeding as many random APKs into fdroid update as possible. On our jenkins server, the tests copy all of the APKs that the jenkins server has generated and builds a repo from them. This process caught lots of little glitches in the whole process. While these little glitches are usually caused by problematic APKs, fdroid update should handle them gracefully. Hopefully this set of fixes accomplishes that.