darcs patch: Add justIf to Data.Maybe

[Henning Thielemann]

On Sat, 22 Aug 2009, Joachim Breitner wrote:

> Hi,
>
> I propose the attached change, with a discussion timeframe until end of
> September. The corresponding ticket is
> http://hackage.haskell.org/trac/ghc/ticket/3446

I proposed the same with reversed parameter order and the name 'toMaybe' 
years ago and it was rejected.

http://www.haskell.org/pipermail/libraries/2004-July/002381.html

However, I have added it to my own utility library.

http://code.haskell.org/~thielema/utility/src/Data/Maybe/HT.hs