Prompt.hs: have historyCompletion filter dupes
Prompt.hs: have historyCompletion filter dupes

Specifically, it calls deleteConsecutiveDuplicates on the end product. uniqSort reverses order in an unfortunate way, so we don't use that.
The use-case is when a user has added the same input many times - as it stands, if the history records 30 'top's or whatever, the completion will show 30 'top' entries! This fixes that.

mathstuf/xmonad-contrib,mathstuf/xmonad-contrib,CaptainPatate/xmonad-contrib,f1u77y/xmonad-contrib,ohlus/xmonad-contrib,ohlus/xmonad-contrib,0/xmonad-contrib,pjones/xmonad-test,CaptainPatate/xmonad-contrib,f1u77y/xmonad-contrib,CaptainPatate/xmonad-contrib,0/xmonad-contrib,ohlus/xmonad-contrib,xmonad/xmonad-contrib,0/xmonad-contrib,mathstuf/xmonad-contrib,xmonad/xmonad-contrib