Context: https://lists.wikimedia.org/pipermail/wikitech-l/2015-May/081644.html
Because the global user merge tool is going to be deployed (and, presumably, used) and WikiGrok stores IDs and names of the users submitting responses, we must update WikiGrok to support merging users.
As @Legoktm's email suggests, this'll entail listening to one of the UserMerge* hooks so that WikiGrok can keep user information up to date. Also, WikiGrok should definitely be listening to the DeleteAccount hook too…
Also, listen to the hooks regardless of whether or not the WikiGrok UI is enabled.