Allow to configure whole branch name (--name / new option)

[blueyed]

Currently you can specify the name, which is used as base of the branch name:

branch = '%s-%s' % (args.name, snapshot.src_path.replace('/', '_'))

Reading the help/code the name option makes a different impression, as if it would allow you to specify the whole name:

    # using the hostname as branch name
    group.add_argument('-n', '--name', default=socket.gethostname(),
                       help="""name of the backup passed to bup,
                               defaults to hostname (%(default)s)""")

What do you think about keeping the current default, but use the name as-is when passed by --name (without the substituted path appended)? (of course, this would be backwards-incompatible)

[anarcat]

how about a new --branch-name argument instead?

[blueyed]

Makes sense. Will you add it or should I create a PR?

[anarcat]

please do :)