[GHC] #9508: Rename package key

[GHC]

#9508: Rename package key
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              Reporter:  ezyang      |            Owner:  ezyang
                  Type:  task        |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.9
            Resolution:              |         Keywords:  backpack
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by simonpj):

 Personally I like "package key".  It's pretty clear that it's something
 you have to look up to find out what it means, and doesn't clash with
 other concepts in GHC/Cabal. (Eg "instance" has many meanings!)

 I could cope with "package instance".  I don't much like "library ID".

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9508#comment:3>
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