Define NameSet.intersectFVs
Define NameSet.intersectFVs

I want it for subsequent commits

olsner/ghc,tjakway/ghcjvm,tjakway/ghcjvm,sdiehl/ghc,snoyberg/ghc,olsner/ghc,vTurbine/ghc,ezyang/ghc,mettekou/ghc,sdiehl/ghc,vikraman/ghc,mettekou/ghc,ezyang/ghc,mettekou/ghc,tjakway/ghcjvm,tjakway/ghcjvm,sgillespie/ghc,snoyberg/ghc,sgillespie/ghc,olsner/ghc,sdiehl/ghc,sgillespie/ghc,vTurbine/ghc,vTurbine/ghc,shlevy/ghc,sdiehl/ghc,mettekou/ghc,ezyang/ghc,sgillespie/ghc,tjakway/ghcjvm,ezyang/ghc,vikraman/ghc,snoyberg/ghc,sgillespie/ghc,vikraman/ghc,snoyberg/ghc,vikraman/ghc,shlevy/ghc,snoyberg/ghc,mettekou/ghc,sdiehl/ghc,vikraman/ghc,shlevy/ghc,mettekou/ghc,snoyberg/ghc,ezyang/ghc,vTurbine/ghc,olsner/ghc,vTurbine/ghc,shlevy/ghc,tjakway/ghcjvm,vikraman/ghc,shlevy/ghc,olsner/ghc,tjakway/ghcjvm,ezyang/ghc,olsner/ghc,olsner/ghc,sdiehl/ghc,mettekou/ghc,sgillespie/ghc,sgillespie/ghc,vikraman/ghc,vTurbine/ghc,shlevy/ghc,snoyberg/ghc,sdiehl/ghc,vTurbine/ghc,ezyang/ghc,shlevy/ghc