Make buildToArrPReprs obey the let/app invariant
Make buildToArrPReprs obey the let/app invariant

Vectorise.Generic.PAMethods.buildToArrPReprs was building an expression like
   pvoids# (lengthSels2# sels)
which does not satisfy the let/app invariant.  It should be more like
  case lengthSels2# sels of l -> pvoids# l

This was caught by Core Lint (once it was taught to check for the invariant)

sdiehl/ghc,vTurbine/ghc,snoyberg/ghc,sdiehl/ghc,vTurbine/ghc,TomMD/ghc,mettekou/ghc,olsner/ghc,vikraman/ghc,mfine/ghc,vikraman/ghc,wxwxwwxxx/ghc,nushio3/ghc,spacekitteh/smcghc,snoyberg/ghc,sgillespie/ghc,sgillespie/ghc,nathyong/microghc-ghc,fmthoma/ghc,siddhanathan/ghc,da-x/ghc,forked-upstream-packages-for-ghcjs/ghc,wxwxwwxxx/ghc,christiaanb/ghc,sgillespie/ghc,acowley/ghc,nushio3/ghc,olsner/ghc,wxwxwwxxx/ghc,acowley/ghc,anton-dessiatov/ghc,acowley/ghc,gcampax/ghc,siddhanathan/ghc,green-haskell/ghc,fmthoma/ghc,GaloisInc/halvm-ghc,siddhanathan/ghc,da-x/ghc,mettekou/ghc,anton-dessiatov/ghc,oldmanmike/ghc,sgillespie/ghc,jstolarek/ghc,oldmanmike/ghc,christiaanb/ghc,da-x/ghc,bitemyapp/ghc,nkaretnikov/ghc,forked-upstream-packages-for-ghcjs/ghc,oldmanmike/ghc,AlexanderPankiv/ghc,green-haskell/ghc,snoyberg/ghc,snoyberg/ghc,mfine/ghc,nathyong/microghc-ghc,ghc-android/ghc,nkaretnikov/ghc,shlevy/ghc,forked-upstream-packages-for-ghcjs/ghc,vikraman/ghc,fmthoma/ghc,gcampax/ghc,vTurbine/ghc,sdiehl/ghc,bitemyapp/ghc,fmthoma/ghc,anton-dessiatov/ghc,fmthoma/ghc,TomMD/ghc,ml9951/ghc,snoyberg/ghc,da-x/ghc,gcampax/ghc,urbanslug/ghc,ezyang/ghc,shlevy/ghc,shlevy/ghc,ezyang/ghc,olsner/ghc,ezyang/ghc,AlexanderPankiv/ghc,ghc-android/ghc,siddhanathan/ghc,urbanslug/ghc,nathyong/microghc-ghc,mcschroeder/ghc,holzensp/ghc,sdiehl/ghc,siddhanathan/ghc,mfine/ghc,wxwxwwxxx/ghc,ghc-android/ghc,GaloisInc/halvm-ghc,nkaretnikov/ghc,nathyong/microghc-ghc,nkaretnikov/ghc,vTurbine/ghc,ml9951/ghc,tjakway/ghcjvm,gridaphobe/ghc,TomMD/ghc,TomMD/ghc,nathyong/microghc-ghc,ml9951/ghc,jstolarek/ghc,vTurbine/ghc,ezyang/ghc,oldmanmike/ghc,gridaphobe/ghc,nkaretnikov/ghc,mcschroeder/ghc,christiaanb/ghc,fmthoma/ghc,gcampax/ghc,GaloisInc/halvm-ghc,anton-dessiatov/ghc,olsner/ghc,holzensp/ghc,gridaphobe/ghc,tjakway/ghcjvm,ml9951/ghc,spacekitteh/smcghc,acowley/ghc,tjakway/ghcjvm,mfine/ghc,oldmanmike/ghc,nathyong/microghc-ghc,TomMD/ghc,anton-dessiatov/ghc,sdiehl/ghc,elieux/ghc,mfine/ghc,da-x/ghc,urbanslug/ghc,ezyang/ghc,urbanslug/ghc,siddhanathan/ghc,da-x/ghc,wxwxwwxxx/ghc,holzensp/ghc,mettekou/ghc,wxwxwwxxx/ghc,forked-upstream-packages-for-ghcjs/ghc,AlexanderPankiv/ghc,shlevy/ghc,christiaanb/ghc,siddhanathan/ghc,urbanslug/ghc,GaloisInc/halvm-ghc,shlevy/ghc,elieux/ghc,bitemyapp/ghc,da-x/ghc,AlexanderPankiv/ghc,gcampax/ghc,ml9951/ghc,green-haskell/ghc,christiaanb/ghc,vikraman/ghc,elieux/ghc,jstolarek/ghc,green-haskell/ghc,acowley/ghc,elieux/ghc,oldmanmike/ghc,shlevy/ghc,mcschroeder/ghc,AlexanderPankiv/ghc,gcampax/ghc,nkaretnikov/ghc,holzensp/ghc,ml9951/ghc,tjakway/ghcjvm,christiaanb/ghc,TomMD/ghc,bitemyapp/ghc,ghc-android/ghc,mfine/ghc,urbanslug/ghc,gcampax/ghc,snoyberg/ghc,elieux/ghc,bitemyapp/ghc,tjakway/ghcjvm,nushio3/ghc,spacekitteh/smcghc,ezyang/ghc,urbanslug/ghc,sdiehl/ghc,nushio3/ghc,forked-upstream-packages-for-ghcjs/ghc,mcschroeder/ghc,mettekou/ghc,sdiehl/ghc,gridaphobe/ghc,spacekitteh/smcghc,spacekitteh/smcghc,elieux/ghc,acowley/ghc,mettekou/ghc,mcschroeder/ghc,tjakway/ghcjvm,vikraman/ghc,nkaretnikov/ghc,fmthoma/ghc,ghc-android/ghc,christiaanb/ghc,mcschroeder/ghc,green-haskell/ghc,forked-upstream-packages-for-ghcjs/ghc,anton-dessiatov/ghc,forked-upstream-packages-for-ghcjs/ghc,vTurbine/ghc,ghc-android/ghc,sgillespie/ghc,vikraman/ghc,GaloisInc/halvm-ghc,ml9951/ghc,ghc-android/ghc,mettekou/ghc,nushio3/ghc,AlexanderPankiv/ghc,anton-dessiatov/ghc,olsner/ghc,acowley/ghc,gridaphobe/ghc,tjakway/ghcjvm,ezyang/ghc,mettekou/ghc,ml9951/ghc,shlevy/ghc,mfine/ghc,gridaphobe/ghc,nushio3/ghc,sgillespie/ghc,sgillespie/ghc,vikraman/ghc,snoyberg/ghc,jstolarek/ghc,oldmanmike/ghc,nushio3/ghc,nathyong/microghc-ghc,olsner/ghc,GaloisInc/halvm-ghc,jstolarek/ghc,elieux/ghc,wxwxwwxxx/ghc,TomMD/ghc,olsner/ghc,vTurbine/ghc,gridaphobe/ghc,AlexanderPankiv/ghc,holzensp/ghc,mcschroeder/ghc,GaloisInc/halvm-ghc