Maintain list of recent nick changes for modules to use

[dgw]

It might be useful to have a list of recent nick changes, for games to use as part of detecting whether or not a "new" user is, in fact, someone who's changed nicks to evade a timer.

Data fields that would be useful:

• timestamp of nick change: modules can use this to ignore old nick changes if they like
• old nickname: modules can look up the old nickname's last-used timestamp
• new nickname: this is probably the dict key, so modules can look up unknown users by nickname
• username & hostname of old nick: modules can use these to confirm a match

It might also be useful simply to provide a convenience method that modules can call to request a check for recent nick-changes from known nicks to the given unknown nick.