[GHC] #9561: Clean up mergeSATInfo

[GHC]

#9561: Clean up mergeSATInfo
-------------------------------------+-------------------------------------
       Reporter:  dfeuer             |                   Owner:
           Type:  task               |                  Status:  new
       Priority:  normal             |               Milestone:  7.8.4
      Component:  Compiler           |                 Version:  7.9
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Easy (less than 1  |         Type of failure:
  hour)                              |  None/Unknown
     Blocked By:                     |               Test Case:
Related Tickets:                     |                Blocking:
                                     |  Differential Revisions:
-------------------------------------+-------------------------------------
 `mergeSATInfo` in SAT.hs is much longer and harder to read than it needs
 to be. I am attaching a patch to make it use `zipWith` instead of zipping
 manually.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9561>
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