[GHC] #9808: Add data-dir to InstalledPackageInfo

[GHC]

#9808: Add data-dir to InstalledPackageInfo
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              Reporter:  luite       |            Owner:  luite
                  Type:  task        |           Status:  new
              Priority:  normal      |        Milestone:  7.10.1
             Component:  Package     |          Version:  7.8.3
  system                             |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:  Phab:D499   |
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Comment (by luite):

 turned out to be not too hard after all, after thomie told me that the
 git.haskell.org/packages/Cabal.git is automatically mirrored from github
 :)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9808#comment:3>
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