[GHC] #9133: Improve parser error reporting in `ghc-pkg`

[GHC]

#9133: Improve parser error reporting in `ghc-pkg`
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       Reporter:  hvr               |             Owner:
           Type:  task              |            Status:  new
       Priority:  normal            |         Milestone:  7.10.1
      Component:  ghc-pkg           |           Version:  7.8.2
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 Here's what I was confronted recently due to a broken sandbox environment:

 {{{
 $ cabal info parsec
 cabal: ghc-pkg: Data.Binary.Get.runGet at position 9583: demandInput: not
 enough bytes
 }}}

 The main problem is that this message is not very helpful (other than
 telling that `ghc-pkg` wasn't able to do something). Duncan told me, that
 the recent `binary` API now provides better facilities for error
 reporting. That could be used to improve the UI of `ghc-pkg` when
 reporting errors.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9133>
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