[GHC] #4806: Make error message more user friendly when module is not found because package is unusable

[GHC]

#4806: Make error message more user friendly when module is not found because
package is unusable
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        Reporter:  mitar             |                Owner:  bollu
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.0.1
      Resolution:                    |             Keywords:  newcomer
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 mpickering):

 They are installed in a completely separate database in ./.cabal-sandbox.
 So they or neither copied nor linked. I haven't understood this ticket but
 it's something that popped into my mind.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4806#comment:20>
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