Internal names list is sometimes out of sync

We've observed that the internal list of usernames (https://github.com/kokarn/KokBot/blob/master/plugins/BotPlug.js#L7) sometimes goes out of sync with the actual users in the channels.

We need to
1. Find out why
2. Fix it

Start at plugins/BotPlug.js line 7 and trace where the internal username list is populated and used, then compare that behavior with the channel users it is meant to represent. Reproduce an out-of-sync case and verify that the list remains aligned with the actual channel users when the fix is complete.

Written by the indexing model from the issue text.