[GHC] #3934: add licence to Windows installer

[GHC]

#3934: add licence to Windows installer
---------------------------------+------------------------------------------
    Reporter:  igloo             |        Owner:  igloo       
        Type:  bug               |       Status:  new         
    Priority:  high              |    Milestone:  6.12.2      
   Component:  Build System      |      Version:  6.12.1      
    Keywords:                    |   Difficulty:              
          Os:  Unknown/Multiple  |     Testcase:              
Architecture:  Unknown/Multiple  |      Failure:  None/Unknown
---------------------------------+------------------------------------------
 Add the licence(s) to the Windows installer. We can probably copy the text
 generation from the OS X installer.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3934>
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