PParser.hs: filename: Explain failed parse with |fail|
PParser.hs: filename: Explain failed parse with |fail|

This still provides misleading output from the parser about what it
was expecting, but does explain what the actual problem was:

    *Pkg.PParser> execout <$> runparser pPkg defaultPkg "foo.ipkg"
                  "package bar\n\nexecutable = \"invalid/filename\""
    Failure foo.ipkg:3:32: error: a filename
        must be non-empty and have no
        directory
        component, expected: space
    executable = "invalid/filename"<EOF>
                                   ^

uuhan/Idris-dev,uuhan/Idris-dev,bravit/Idris-dev,aaronc/Idris-dev,FranklinChen/Idris-dev,bravit/Idris-dev,eklavya/Idris-dev,bravit/Idris-dev,tpsinnem/Idris-dev,FranklinChen/Idris-dev,TimRichter/Idris-dev,adnelson/Idris-dev,markuspf/Idris-dev,markuspf/Idris-dev,jmitchell/Idris-dev,adnelson/Idris-dev,eklavya/Idris-dev,adnelson/Idris-dev,aaronc/Idris-dev,ozgurakgun/Idris-dev,aaronc/Idris-dev,jeremy-w/Idris-dev,lenary/Idris-dev,KaneTW/Idris-dev,markuspf/Idris-dev,bravit/Idris-dev,enolan/Idris-dev,aaronc/Idris-dev,eklavya/Idris-dev,aaronc/Idris-dev,KaneTW/Idris-dev,kojiromike/Idris-dev,tpsinnem/Idris-dev,kojiromike/Idris-dev,mrmonday/Idris-dev,ben-schulz/Idris-dev,ozgurakgun/Idris-dev,aaronc/Idris-dev,jeremy-w/Idris-dev,uuhan/Idris-dev,KaneTW/Idris-dev,jeremy-w/Idris-dev,uuhan/Idris-dev,TimRichter/Idris-dev,tpsinnem/Idris-dev,TimRichter/Idris-dev,kojiromike/Idris-dev,mrmonday/Idris-dev,shlevy/Idris-dev,shlevy/Idris-dev,ben-schulz/Idris-dev,jeremy-w/Idris-dev,jmitchell/Idris-dev,markuspf/Idris-dev,mpkh/Idris-dev,mrmonday/Idris-dev,enolan/Idris-dev,markuspf/Idris-dev,mrmonday/Idris-dev,lenary/Idris-dev,kojiromike/Idris-dev,mpkh/Idris-dev,TimRichter/Idris-dev,mrmonday/Idris-dev,kojiromike/Idris-dev,adnelson/Idris-dev,Heather/Idris-dev,bravit/Idris-dev,markuspf/Idris-dev,ben-schulz/Idris-dev,enolan/Idris-dev,mrmonday/Idris-dev,lenary/Idris-dev,Heather/Idris-dev,ozgurakgun/Idris-dev,eklavya/Idris-dev,uuhan/Idris-dev,enolan/Idris-dev,jmitchell/Idris-dev,enolan/Idris-dev,KaneTW/Idris-dev,ben-schulz/Idris-dev,eklavya/Idris-dev,lenary/Idris-dev,ozgurakgun/Idris-dev,shlevy/Idris-dev,tpsinnem/Idris-dev,lenary/Idris-dev,adnelson/Idris-dev,bravit/Idris-dev,lenary/Idris-dev,tpsinnem/Idris-dev,Heather/Idris-dev,mpkh/Idris-dev,ozgurakgun/Idris-dev,TimRichter/Idris-dev,shlevy/Idris-dev,FranklinChen/Idris-dev,TimRichter/Idris-dev,jmitchell/Idris-dev,markuspf/Idris-dev,mpkh/Idris-dev,jmitchell/Idris-dev,FranklinChen/Idris-dev,shlevy/Idris-dev,eklavya/Idris-dev,ozgurakgun/Idris-dev,KaneTW/Idris-dev,KaneTW/Idris-dev,ben-schulz/Idris-dev,Heather/Idris-dev,uuhan/Idris-dev,shlevy/Idris-dev,FranklinChen/Idris-dev,Heather/Idris-dev,mpkh/Idris-dev,ben-schulz/Idris-dev,FranklinChen/Idris-dev,jeremy-w/Idris-dev,enolan/Idris-dev,uuhan/Idris-dev,jeremy-w/Idris-dev,adnelson/Idris-dev,kojiromike/Idris-dev,jmitchell/Idris-dev,mpkh/Idris-dev,tpsinnem/Idris-dev,Heather/Idris-dev