Code review comment for lp:~jtv/launchpad/bug-499405-translationtemplates-buildmanager

I conferenced with abentley about this, so it's not just me saying "please use bzrlib" but also another code folk. If nothing else, it gives us a nice traceback, instead of a user friendly (and rather unhelpful) error message. It basically runs bzr as a subprocess, which could actually make things more complicated.