Added some 7.7/7.8 functions and instances.

Hi,

I had [raised this question on haskell-cafe](http://www.haskell.org/pipermail/haskell-cafe/2014-January/112228.html), and perhaps rather hastily, after no answer for a while, published [this](https://github.com/jcristovao/BaseFuture), only to find out later that you had already something identical going on.

This pull request adds some of the new functions and instances currently in GHC Head, ones that I needed and (others) that did not seem controversial.

I've added some tests already, but I'm not sure if you have any reservations to having GHC Head code in here, so please tell me if this is OK, and if you require the remaining tests.

Thanks!