[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
---------------------------------+------------------------------------------
    Reporter:  mitar             |       Owner:              
        Type:  feature request   |      Status:  new         
    Priority:  normal            |   Component:  Compiler    
     Version:  7.0.1             |    Keywords:              
    Testcase:                    |   Blockedby:              
          Os:  Unknown/Multiple  |    Blocking:              
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown
---------------------------------+------------------------------------------
 Make error message more user friendly when module is not found because
 package is unusable. Currently it just reports that module is missing (the
 same as it even would not be installed) but then checking with `ghc-pkg
 find-module` shows package correctly. Chasing '-v' output around can then
 show you this but it would be easier that you would immediately get a
 helpful message.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4806>
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