[GHC] #8595: add fusion RULES for mapMaybe

[GHC]

#8595: add fusion RULES for mapMaybe
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        Reporter:  akio              |            Owner:  nomeata
            Type:  feature request   |           Status:  patch
        Priority:  normal            |        Milestone:
       Component:  libraries/base    |          Version:  7.6.3
      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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Changes (by nomeata):

 * owner:   => nomeata


Comment:

 I’ll validate and push this later today.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8595#comment:2>
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