failWithM polymorphic in the returning monad

I've stumbled upon an issue which is best described by my stackoverflow question:

http://stackoverflow.com/questions/37515246/using-failwith-with-servant-and-custom-monad-stack

One of the answers suggested rolling own helper:

``` haskell
(!??) :: MonadError e m => m (Maybe a) -> e -> m a
act !?? err = act >>= maybe (throwError err) return
```

I'm not that proficient in transformers stacks, and I bet the aim of this library is to help people like me, so what would be the chances of including thing like that? Would it supersede the existing `!?` or would it have to be separate helper?

Start by reading the existing `!?` helper and the linked Stack Overflow question to understand the proposed `MonadError` behavior. Determine whether the request is a replacement or a separate helper; done requires an agreed API direction and the corresponding library change.

Written by the indexing model from the issue text.