Adds a junction to the _current_statement.

def _add_junction(item):
    '''
    Adds a junction to the _current_statement.
    '''
    type_, channels = _expand_one_key_dictionary(item)
    junction = UnnamedStatement(type='junction')
    for item in channels:
        type_, value = _expand_one_key_dictionary(item)
        channel = UnnamedStatement(type='channel')
        for val in value:
            if _is_reference(val):
                _add_reference(val, channel)
            elif _is_inline_definition(val):
                _add_inline_definition(val, channel)
        junction.add_child(channel)
    _current_statement.add_child(junction)