Code review comment for lp:~mbp/bzr/45719-update-r

This adds a 'bzr update -r' option. If the branch is bound to another, it always updates from the master branch first. This updated form of the patch addresses John's review comments in <https://bugs.edge.launchpad.net/bzr/+bug/45719/comments/20>.

This is an updated version of what was one of the longest-standing merges, and it's for a five-digit bug too <https://bugs.edge.launchpad.net/bzr/+bug/45719>.