'Returns true if all the paths have the same leading path name
(i.e., everything is in one subdirectory in an archive)'

def has_leading_dir(self, paths):

    common_prefix = None
    for path in paths:
        (prefix, rest) = self.split_leading_dir(path)
        if (not prefix):
            return False
        elif (common_prefix is None):
            common_prefix = prefix
        elif (prefix != common_prefix):
            return False
    return True
