[GHC] #9265: Create PackageKey to replace PackageId, including version dependency information (was: Extend PackageId to include version dependency information)

[GHC]

#9265: Create PackageKey to replace PackageId, including version dependency
information
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              Reporter:  ezyang      |            Owner:  ezyang
                  Type:  feature     |           Status:  new
  request                            |        Milestone:  7.10.1
              Priority:  high        |          Version:  7.9
             Component:  Package     |         Keywords:  backpack
  system                             |     Architecture:  Unknown/Multiple
            Resolution:              |       Difficulty:  Unknown
      Operating System:              |       Blocked By:
  Unknown/Multiple                   |  Related Tickets:
       Type of failure:              |
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9265#comment:9>
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