[GHC] #3492: Add TyThing -> HsSyn translation code from Haddock

[GHC]

#3492: Add TyThing -> HsSyn translation code from Haddock
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  Reporter:  simonmar          |          Owner:                  
      Type:  task              |         Status:  new             
  Priority:  normal            |      Milestone:  6.14.1          
 Component:  Compiler          |        Version:  6.10.4          
  Severity:  normal            |       Keywords:                  
Difficulty:  Unknown           |       Testcase:                  
        Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
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 See attached; part of refactoring described in
 [wiki:Commentary/Compiler/TemplateHaskell].

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3492>
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