Generalise 'waitAny' & co to use Foldable

[sheaf]

The following functions used to expect a list of Async computations as input, but have been generalised to work with a Foldable constraint:

• waitAny, waitAnySTM, waitAnyCancel,
• waitAnyCatch, waitAnyCatchSTM, waitAnyCatchCancel.

This extra generality is useful when dealing with a Set of Async computations.

[simonmar]

I think we should also SPECIALIZE waitAnySTM and waitAnyCatchSTM to lists to avoid any performance regressions from the extra overloading.

[phadej]

This is a breaking change.

E.g.

{-# LANGUAGE OverloadedLists #-}

...
   res <- waitAnyCatch [x, y] 

or any other polymorphic argument (forced now by waitAnyCatch to be lists) will fail.