[GHC] #10890: Incorrect redundant import warning for type classes

[GHC]

#10890: Incorrect redundant import warning for type classes
-------------------------------------+-------------------------------------
        Reporter:  quchen            |                   Owner:
            Type:  bug               |                  Status:  patch
        Priority:  normal            |               Milestone:  8.0.1
       Component:  Compiler          |                 Version:  7.10.2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:  D1257
-------------------------------------+-------------------------------------
Changes (by osa1):

 * status:  new => patch
 * differential:   => D1257


Comment:

 Thanks to @quchen for realizing that my patch reduces to previous version
 if there's only one imported `RdrName` with same name. I created a patch
 for this and I'll be adding tests soon.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10890#comment:10>
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