When leaving a comment, users are given the option of providing a
homepage to link their name to. A common error is to just provide a
domain like "oddmuse.org" instead of a real URL. The resulting markup
used to be [oddmuse.org YourName] which doesn't do what the user
expected. That's why a piece of code used to check whether the homepage
starts with "http://" and if it doesn't, it prefixes it, resulting in
"[http://oddmuse.org YourName]". If the homepage started with
"https://", however, the code did the wrong thing. That's why we're now
checking whether the homepage starts with any known URL-protocol and a
colon.
