Code review comment for ~ahasenack/ubuntu/+source/tdb:disco-tdb-1.3.18

From IRC:
<cjwatson> bzr-git's tdb thing is used by LP
<cjwatson> for git-to-bzr code imports
<cjwatson> this doesn't mean you should block on it, since we maintain our own copies of the modules we need, just FYI on what sorts of things it's used for