Small improvement to CorePrep
Small improvement to CorePrep

This change avoids unnecessary bindings. Example

     foo (let fn = \x.blah in
          in fn)

We were generating something stupid like

    let fn = \x.blah in
    let fn' = \eta. fn eta
    in foo fn

Now we don't.  The change is quite small.

Thanks to Ben for showing me an example of this happening.

tibbe/ghc,gcampax/ghc,holzensp/ghc,mettekou/ghc,nomeata/ghc,TomMD/ghc,oldmanmike/ghc,tjakway/ghcjvm,GaloisInc/halvm-ghc,urbanslug/ghc,nushio3/ghc,tibbe/ghc,ryantm/ghc,gridaphobe/ghc,TomMD/ghc,snoyberg/ghc,fmthoma/ghc,green-haskell/ghc,ml9951/ghc,mcmaniac/ghc,nushio3/ghc,bitemyapp/ghc,shlevy/ghc,tjakway/ghcjvm,acowley/ghc,tibbe/ghc,GaloisInc/halvm-ghc,AlexanderPankiv/ghc,olsner/ghc,siddhanathan/ghc,vikraman/ghc,mettekou/ghc,gridaphobe/ghc,tjakway/ghcjvm,acowley/ghc,AlexanderPankiv/ghc,nkaretnikov/ghc,tjakway/ghcjvm,mcschroeder/ghc,ezyang/ghc,da-x/ghc,TomMD/ghc,wxwxwwxxx/ghc,oldmanmike/ghc,nkaretnikov/ghc,christiaanb/ghc,oldmanmike/ghc,mfine/ghc,shlevy/ghc,forked-upstream-packages-for-ghcjs/ghc,vTurbine/ghc,mcmaniac/ghc,ml9951/ghc,holzensp/ghc,lukexi/ghc-7.8-arm64,forked-upstream-packages-for-ghcjs/ghc,AlexanderPankiv/ghc,ghc-android/ghc,spacekitteh/smcghc,vTurbine/ghc,nushio3/ghc,mcmaniac/ghc,tibbe/ghc,frantisekfarka/ghc-dsi,mfine/ghc,forked-upstream-packages-for-ghcjs/ghc,ml9951/ghc,ghc-android/ghc,AlexanderPankiv/ghc,hferreiro/replay,TomMD/ghc,shlevy/ghc,siddhanathan/ghc,anton-dessiatov/ghc,oldmanmike/ghc,lukexi/ghc-7.8-arm64,sgillespie/ghc,vikraman/ghc,TomMD/ghc,acowley/ghc,bitemyapp/ghc,vikraman/ghc,ghc-android/ghc,anton-dessiatov/ghc,fmthoma/ghc,ekmett/ghc,ekmett/ghc,anton-dessiatov/ghc,ezyang/ghc,wxwxwwxxx/ghc,siddhanathan/ghc,tibbe/ghc,olsner/ghc,urbanslug/ghc,sdiehl/ghc,nkaretnikov/ghc,anton-dessiatov/ghc,TomMD/ghc,ghc-android/ghc,olsner/ghc,spacekitteh/smcghc,mettekou/ghc,sdiehl/ghc,vTurbine/ghc,olsner/ghc,lukexi/ghc,green-haskell/ghc,ryantm/ghc,ekmett/ghc,snoyberg/ghc,sgillespie/ghc,da-x/ghc,tjakway/ghcjvm,jstolarek/ghc,frantisekfarka/ghc-dsi,snoyberg/ghc,nathyong/microghc-ghc,green-haskell/ghc,olsner/ghc,christiaanb/ghc,ilyasergey/GHC-XAppFix,lukexi/ghc,elieux/ghc,oldmanmike/ghc,jstolarek/ghc,ilyasergey/GHC-XAppFix,nushio3/ghc,fmthoma/ghc,acowley/ghc,frantisekfarka/ghc-dsi,lukexi/ghc-7.8-arm64,nkaretnikov/ghc,hferreiro/replay,forked-upstream-packages-for-ghcjs/ghc,shlevy/ghc,ml9951/ghc,gcampax/ghc,bitemyapp/ghc,gcampax/ghc,AlexanderPankiv/ghc,spacekitteh/smcghc,holzensp/ghc,nkaretnikov/ghc,ml9951/ghc,mettekou/ghc,frantisekfarka/ghc-dsi,ml9951/ghc,bitemyapp/ghc,forked-upstream-packages-for-ghcjs/ghc,mcschroeder/ghc,gcampax/ghc,tjakway/ghcjvm,ezyang/ghc,oldmanmike/ghc,mfine/ghc,mcschroeder/ghc,elieux/ghc,sdiehl/ghc,bitemyapp/ghc,hferreiro/replay,elieux/ghc,sdiehl/ghc,gridaphobe/ghc,oldmanmike/ghc,mettekou/ghc,vikraman/ghc,ghc-android/ghc,ilyasergey/GHC-XAppFix,green-haskell/ghc,tjakway/ghcjvm,vikraman/ghc,GaloisInc/halvm-ghc,mcschroeder/ghc,GaloisInc/halvm-ghc,jstolarek/ghc,nomeata/ghc,TomMD/ghc,gcampax/ghc,gcampax/ghc,fmthoma/ghc,christiaanb/ghc,wxwxwwxxx/ghc,nushio3/ghc,AlexanderPankiv/ghc,snoyberg/ghc,snoyberg/ghc,ezyang/ghc,ghc-android/ghc,nkaretnikov/ghc,gridaphobe/ghc,da-x/ghc,forked-upstream-packages-for-ghcjs/ghc,mcmaniac/ghc,lukexi/ghc-7.8-arm64,sgillespie/ghc,anton-dessiatov/ghc,ezyang/ghc,vTurbine/ghc,sgillespie/ghc,frantisekfarka/ghc-dsi,sgillespie/ghc,anton-dessiatov/ghc,jstolarek/ghc,ghc-android/ghc,hferreiro/replay,GaloisInc/halvm-ghc,mcschroeder/ghc,da-x/ghc,sdiehl/ghc,gridaphobe/ghc,vTurbine/ghc,lukexi/ghc-7.8-arm64,urbanslug/ghc,mcschroeder/ghc,vTurbine/ghc,shlevy/ghc,hferreiro/replay,ryantm/ghc,da-x/ghc,snoyberg/ghc,acowley/ghc,shlevy/ghc,forked-upstream-packages-for-ghcjs/ghc,wxwxwwxxx/ghc,olsner/ghc,ryantm/ghc,wxwxwwxxx/ghc,holzensp/ghc,gridaphobe/ghc,urbanslug/ghc,nathyong/microghc-ghc,vikraman/ghc,lukexi/ghc,da-x/ghc,AlexanderPankiv/ghc,mettekou/ghc,nkaretnikov/ghc,elieux/ghc,olsner/ghc,nathyong/microghc-ghc,ezyang/ghc,nathyong/microghc-ghc,fmthoma/ghc,hferreiro/replay,spacekitteh/smcghc,elieux/ghc,ryantm/ghc,siddhanathan/ghc,sgillespie/ghc,nomeata/ghc,sdiehl/ghc,wxwxwwxxx/ghc,ezyang/ghc,spacekitteh/smcghc,green-haskell/ghc,nomeata/ghc,fmthoma/ghc,elieux/ghc,lukexi/ghc,mfine/ghc,urbanslug/ghc,mettekou/ghc,jstolarek/ghc,nushio3/ghc,elieux/ghc,anton-dessiatov/ghc,nathyong/microghc-ghc,ml9951/ghc,holzensp/ghc,siddhanathan/ghc,mfine/ghc,nomeata/ghc,snoyberg/ghc,wxwxwwxxx/ghc,GaloisInc/halvm-ghc,vikraman/ghc,acowley/ghc,christiaanb/ghc,gridaphobe/ghc,urbanslug/ghc,sgillespie/ghc,lukexi/ghc,vTurbine/ghc,christiaanb/ghc,hferreiro/replay,acowley/ghc,GaloisInc/halvm-ghc,nathyong/microghc-ghc,christiaanb/ghc,gcampax/ghc,fmthoma/ghc,sdiehl/ghc,ilyasergey/GHC-XAppFix,ml9951/ghc,mfine/ghc,ekmett/ghc,ekmett/ghc,christiaanb/ghc,da-x/ghc,shlevy/ghc,siddhanathan/ghc,mcschroeder/ghc,nushio3/ghc,siddhanathan/ghc,mcmaniac/ghc,nathyong/microghc-ghc,mfine/ghc,urbanslug/ghc