Code review comment for lp:~twom/launchpad/precache-gitrepository-branch-queries

I agree with your comment on IRC that it seems like you have too many calls to `clear_property_cache`, and I think that's because you're doing this slightly too far up the call stack. Try instead doing this in `make_merge_proposal_without_reviewers`, though in a more targeted form: `del get_property_cache(proposal).votes` after removing the votes. Then try removing all your `clear_property_cache` calls and see which ones you really need after that.