Fix #1380

Add No Prefix and Any Prefix filter/sort options.
https://github.com/mybb/mybb/issues/1380
> Don't you know how isset works?

I know what isset is used for, do you know the reason it being used here @Destroy666x? Apparently you don't.
https://github.com/mybb/mybb/blob/master/forumdisplay.php#L405
http://community.mybb.com/thread-119721.html
community.mybb.com/thread-125279.html

> the variable is always isset for users

False. *hint*guests*hint*

Why don't you stop making assumptions you are not qualified to do? Or at least be, don't know, kind? I should had been more clear instead of throwing my comment there, but even so..

> Did you at least test it?

Yes, I took the time to test you implementation and apart from those, unnecessary changes (this being the important one), it works. I will kindly keep reviewing your code, you welcome and thanks.