branch-puller lacks end-to-end tests

I recently go a patch through review and pqm that "fixed" the branch puller into requiring that source locations be always URI. But the authserver gives absolute paths as source for hosted branches. So rolling out this change without fixing it would have broken the branch hosting service. If there had been some end-to-end test for the branch puller, the problem would have been detected earlier, or at worst it would have require a simultaneous update of the authserver and the branch puller.

The branch-puller needs end-to-end tests. The list of branches starting with rows in the database, going through the authserver, the xmlrpc, and finally the branch-puller script. The branch data starting from the filesystem (for hosted branches) and one or two http servers (for import and mirror branches) and copied to the filesystem.