[GHC] #9508: Rename package key

[GHC]

#9508: Rename package key
-------------------------------------+-------------------------------------
              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:              |
-------------------------------------+-------------------------------------

Comment (by ezyang):

 Simon Marlow quite dislikes it, because it implies that it is the "primary
 key" to the package database, but it actually isn't: the primary key of
 the package database is the installed package ID.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9508#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler