revbranchcache: store repo on the object Previously we would instantiate the revbranchcache with a repo object, use it briefly, then require it be passed in every time we wanted to fetch any information. This seems unnecessary since it's obviously specific to that repo (since it was constructed with it). This patch stores the repo on the revbranchcache object, and removes the repo parameter from the various functions on that class. This has the other nice benefit of removing the double-revbranchcache-read that existed before (it was read once for the branch revset, and once for the repo.revbranchcache).