config_list can set invalid values and break lists.

[Mark Sapiro]

config_list can set list attributes to invalid values. For example, the list's topics attribute is a list of 4-tuples. it is possible with config_list to set topics to, e.g., a string or a list of strings. Doing this will cause Mailman.MailList.CheckValues() to throw a ValueError. This is a serious issue as it breaks everything that tries to instantiate all lists such as the listinfo overview.

I'm not going to attempt to fix this in config_list, but I will fix CheckValues() to not throw the uncaught ValueError() if topics is not a list of 4-tuples.