Bug: links like these returned 404s:
* https://danbooru.donmai.us/wiki_pages/...
* https://danbooru.donmai.us/wiki_pages/.hack//
* https://danbooru.donmai.us/wiki_pages/ssss.gridman
Cause: by default, Rails uses dots in route segments to separate the id
from the format. For example, in /wiki_pages/ssss.gridman, the id is
parsed as "ssss" and the format is "gridman" (as if "gridman" were a
format like "json" or "xml").
We work around this by specifying the regex for the id param manually.
The trick here is to use a non-greedy match-all combined with a positive
lookahead to detect the extension but not include it in the match.
a653513e0a