Check that the tgt's submodule is included by src, if they belong
    to the same module.

def is_submodule_included(src, tgt):
    """Check that the tgt's submodule is included by src, if they belong
    to the same module."""
    if tgt is None or not hasattr(tgt, 'i_orig_module'):
        return True
    if (tgt.i_orig_module.keyword == 'submodule' and
        src.i_orig_module != tgt.i_orig_module and
        src.i_orig_module.i_modulename == tgt.i_orig_module.i_modulename):
        if src.i_orig_module.search_one('include',
                                        tgt.i_orig_module.arg) is None:
            return False
    return True