multi-pull should support specifying pull order

Currently mult-pull seems to pull branches in alphabetical order. In some setups it may be that under a repo, one branch is from a remote trunk and there are multiple local feature branches from trunk. As there is no guarantee trunk is pulled first we need to run the command twice to get the latest updates.

It would be nice if the order of pull could somehow be specified to multi-branch.

One option would be:
$ bzr multi-pull <location> [dirs]

Alternatively,
$ bzr multi-pull [location] --first dir

The latter could be used to specify which branch to pull first.