Improve (and simplify) the short-circuiting of Refl coercions
Improve (and simplify) the short-circuiting of Refl coercions

The constraint solver sometimes goes to a lot of effort that turns
out to be Refl in the end, and avoiding zonking those proofs is a
useful optimisation. (Trac #5030)

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