[GHC] #11782: Teach ghc-pkg to read multiple registrations from command line

[GHC]

#11782: Teach ghc-pkg to read multiple registrations from command line
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        Reporter:  ezyang            |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  ghc-pkg           |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by hvr):

 IOW, `ghc-pkg register` will be able to read the output of `ghc-pkg dump`?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11782#comment:2>
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