CommandRunner throws KeyError

[Mark Sapiro]

If a message to the list-request contains a line that would be a command but has the command word terminated with a dot, e.g. a line like

Help. Please unsubscribe me

CommandRunner can throw KeyError. I.e., in this example, it sets modname to 'Mailman.Commands.cmd_help.' and __import__(modname) succeeds, but handler = sys.modules[modname] then throws KeyError because of the trailing dot.