Proposal: add handleError to mtl

[Ross Paterson]

On Wed, Jun 05, 2013 at 01:50:01PM -0400, Edward Kmett wrote:
> Sure. I can see merit to consistency with base in this regard. 
> 
> I would like a version of it in transformers monomorphized to the particular ErrorT monad though as well for consistency. Does that mean we'd want a liftHandle to avoid doing a lot of flipping with liftCatch?

For the monomorphic version, it's probably best to keep these lifts to a
minimum, and use flip on liftCatch.

On the subject of ErrorT, I wonder if it's time to deprecate the Error class.