'From the output of pylint msg, to a dict, where each key
is a unique error identifier, value is a list of LintOutput'

@classmethod
def from_msg_to_dict(cls, msg):

    result = {}
    for line in msg.splitlines():
        obj = cls.from_line(line)
        if obj.is_ignored():
            continue
        key = obj.key()
        if (key not in result):
            result[key] = []
        result[key].append(obj)
    return result
