lp-propose $BRANCH always prefers the parent branch

[John A Meinel]

lp-propose uses this logic:
@staticmethod
def candidate_urls(bzr_branch):
    """Iterate through related URLs that might be Launchpad URLs.

    :param bzr_branch: A Bazaar branch to find URLs from.
    :return: a generator of URL strings.
    """
    url = bzr_branch.get_public_branch()
    if url is not None:
        yield url
    url = bzr_branch.get_push_location()
    if url is not None:
        yield url
    url = bzr_branch.get_parent()
    if url is not None:
        yield url
    yield bzr_branch.base

But that means if you do 'bzr lp-propose lp:~an/lp/branch' it will actually target that branch's parent. (So people who do: bzr branch lp:project lp:maintenance/series will end up having 'lp-propose lp:maintenance/series' targetting the trunk branch by default.)

You can get around this by setting a 'public_branch' the maintenance branch. However it seems non-obvious that manually specifying a branch would not use that branch.

I think it makes the most sense to stop using parent_branch by default. Even in the local mirror case it is only sometimes right. Having someone uses 'bzr config public_branch=...' if they want to use a local mirror seems better than having to set that for doing 'bzr lp-propose lp:project' or 'lp:project/series' not doing what you expect.