Support for Curry (functional logic language based on Haskell)

I was going through the repositories to see if there was any unmerged code lying around, and I found @marco-comini's 2fffd00d88a41bea4c35f221f991c048a56fab5d commit. It adds support for the Curry programming language. This was requested before in http://trac.haskell.org/haskell-src-exts/ticket/54. I rebased the patch to master and here it is. It's not ready to merge yet; there are a few -Wall things, exact printing is missing/broken, and of course it needs tests. My near-term plans don't include finishing it, although I might come back in a few years, or if someone else wants to finish it they're welcome to.