Sometimes people send multiple tickets saying the same thing

Notes:
* Probably only works if the creators of each ticket are watchers/CC's in the other ticket
* Messages are combined and sorted chronologically
* Tags are combined
** Namespaced tags are kept for the "winning" ticket
* The creator of the "winning" ticket is used, other CC's/watchers are combined
* Assignee, priority, status, etc., are kept for the "winning" ticket.