[GHC] #12637: ghc-pkg: Allow unregistering multiple packages in one call

[GHC]

#12637: ghc-pkg: Allow unregistering multiple packages in one call
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        Reporter:  nh2               |                Owner:
            Type:  feature request   |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  D2550
       Wiki Page:                    |
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Comment (by nh2):

 This turns out quite easy, I've attached a patch.

 In a future iteration of this, it would be a nice-to-have if it could
 automatically figure out in which order to unregister, but that's for
 later.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12637#comment:2>
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