Initial branch doesn't copy tags

[John A Meinel]

Encountered while debugging: bug #745664

a_branch.bzrdir.sprout('target').open_branch()

Does not copy the tags from a_branch. This is because the copying of tags is done in Branch.pull(), which is *not* used by sprout(). Instead, sprout() directly calls target.repository.fetch(source) and then does Branch.initialize() after the fetch has completed.