[GHC] #9178: improve orphan instance warning

[GHC]

#9178: improve orphan instance warning
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        Reporter:  fphh              |            Owner:
            Type:  task              |           Status:  patch
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.8.2
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by Joachim Breitner <mail@…>):

 In [changeset:"877a9577280f4b6aa6ef47f7a27d9b741b8234cf/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="877a9577280f4b6aa6ef47f7a27d9b741b8234cf"
 Better warning message for orphan instances (Ticket #9178)

 Including a test case.
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9178#comment:4>
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