def register(command):
def wrapper(subcommand):<EOL><INDENT>command.add_subcommand(subcommand)<EOL>return subcommand<EOL><DEDENT>return wrapper<EOL>
Register a command with a parent command.

    The ``register`` decorator decorates a Command instance (not a function).
    It is intended to be used with the ``command`` decorator (which decorates a
    function and returns a Command instance).

    Args
    ----
    comand : Command
        The parent command.

    Example
    -------
    .. testcode::

       mygit = Command(name='status')

       @register(mygit)
       @command('status')
       def status():
           print 'Nothing to commit.'

    .. doctest::
       :hide:

       >>> mygit.init()
       >>> mygit.parse_args(['status'])
       Nothing to commit.