[GHC] #10755: Add `MonadPlus IO` and `Alternative IO` instances

[GHC]

#10755: Add `MonadPlus IO` and `Alternative IO` instances
-------------------------------------+-------------------------------------
        Reporter:  hvr               |                   Owner:
            Type:  task              |                  Status:  patch
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Core Libraries    |                 Version:
      Resolution:                    |                Keywords:  report-
                                     |  impact
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:  Phab:D1148
-------------------------------------+-------------------------------------

Comment (by ekmett):

 I think the ideal situation would be to have `transformers` continue to
 export those instances conditional on the version of `base`.

 This would ensure that the maximal number of versions of `base` work with
 the maximal number of versions of `transformers`, rather than inducing an
 unneeded gate function on what works with what.

 These sorts of gotchas are the things that drive away users, so it is
 worth spending the time to get this right.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10755#comment:8>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler