[GHC] #973: Adding Arbitrary instance for Either

[GHC]

#973: Adding Arbitrary instance for Either
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    Reporter:  guest              |       Owner:         
        Type:  proposal           |      Status:  new    
    Priority:  normal             |   Milestone:         
   Component:  libraries (other)  |     Version:  6.6    
    Severity:  normal             |    Keywords:         
  Difficulty:  Unknown            |    Testcase:         
Architecture:  Unknown            |          Os:  Unknown
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Have Either a b be an instance of Arbitrary when both a and b are
 instances of Arbitrary.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/973>
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