[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:  (none)
            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):  Phab:D4783
       Wiki Page:                    |
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Comment (by sgillespie):

 I added my phabricator revision, but it doesn't appear to be building
 (we're on Step 1 for over 24 hours now):
 https://phabricator.haskell.org/harbormaster/build/47009/

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4806#comment:30>
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