Username is case-sensitive

[Nightcaat]

I can't log in as "nightcat" and I assume that someone would be able to register as "nightcat" so please fix that!

[y21]

You can't login? What error does it give to you?

[Nightcaat]

It just says "Incorrect username or password."

[y21]

Oh, I totally got it wrong. I know what you mean. Good idea!

[y21]

Fixed in daa0ec3; it now checks if the username already exists, no matter if the original name has different capitalization.
In other words: nobody will be able to register as nightcat or NIGhtCaT.

[Nightcaat]

Registration works as intended, but I can still only log in as Nightcat.