[GHC] #3085: warn about language extensions that are not used

[GHC]

#3085: warn about language extensions that are not used
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    Reporter:  PVerswyvelen                  |        Owner:              
        Type:  feature request               |       Status:  new         
    Priority:  normal                        |    Milestone:  7.0.1       
   Component:  Compiler                      |      Version:  6.10.1      
    Keywords:  warnings extensions language  |     Testcase:              
   Blockedby:                                |   Difficulty:  Unknown     
          Os:  Unknown/Multiple              |     Blocking:              
Architecture:  Unknown/Multiple              |      Failure:  None/Unknown
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Changes (by liyang):

 * cc: hackage.haskell.org@… (added)


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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3085#comment:23>
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