ClangImporter: Tighten up isMethodAlreadyImported()
ClangImporter: Tighten up isMethodAlreadyImported()

Allow two methods to be imported with the same selector, as long as they
have different Swift DeclNames. This is required for lazy mirrored protocol
member loading to work correctly, so that the same declarations are
imported regardless of name lookup order. The commit for the mirrored
protocol member change will have test cases that cover this behavior.

ahoppen/swift,harlanhaskins/swift,airspeedswift/swift,aschwaighofer/swift,harlanhaskins/swift,tkremenek/swift,parkera/swift,parkera/swift,jckarter/swift,benlangmuir/swift,jckarter/swift,stephentyrone/swift,benlangmuir/swift,aschwaighofer/swift,harlanhaskins/swift,roambotics/swift,airspeedswift/swift,allevato/swift,parkera/swift,atrick/swift,glessard/swift,CodaFi/swift,jmgc/swift,harlanhaskins/swift,allevato/swift,stephentyrone/swift,gregomni/swift,ahoppen/swift,gregomni/swift,airspeedswift/swift,glessard/swift,aschwaighofer/swift,nathawes/swift,apple/swift,jckarter/swift,gregomni/swift,allevato/swift,gregomni/swift,nathawes/swift,ahoppen/swift,hooman/swift,roambotics/swift,CodaFi/swift,harlanhaskins/swift,airspeedswift/swift,parkera/swift,stephentyrone/swift,glessard/swift,allevato/swift,ahoppen/swift,jmgc/swift,atrick/swift,JGiola/swift,roambotics/swift,allevato/swift,rudkx/swift,roambotics/swift,hooman/swift,stephentyrone/swift,jmgc/swift,roambotics/swift,CodaFi/swift,allevato/swift,parkera/swift,parkera/swift,tkremenek/swift,harlanhaskins/swift,parkera/swift,nathawes/swift,airspeedswift/swift,benlangmuir/swift,CodaFi/swift,aschwaighofer/swift,apple/swift,tkremenek/swift,rudkx/swift,CodaFi/swift,atrick/swift,apple/swift,airspeedswift/swift,JGiola/swift,apple/swift,roambotics/swift,atrick/swift,hooman/swift,jckarter/swift,aschwaighofer/swift,jmgc/swift,hooman/swift,glessard/swift,jmgc/swift,harlanhaskins/swift,JGiola/swift,CodaFi/swift,xwu/swift,tkremenek/swift,gregomni/swift,parkera/swift,JGiola/swift,jckarter/swift,jckarter/swift,aschwaighofer/swift,jckarter/swift,stephentyrone/swift,tkremenek/swift,xwu/swift,hooman/swift,apple/swift,ahoppen/swift,stephentyrone/swift,CodaFi/swift,xwu/swift,stephentyrone/swift,xwu/swift,gregomni/swift,rudkx/swift,atrick/swift,nathawes/swift,glessard/swift,glessard/swift,hooman/swift,rudkx/swift,rudkx/swift,jmgc/swift,JGiola/swift,xwu/swift,tkremenek/swift,rudkx/swift,JGiola/swift,nathawes/swift,nathawes/swift,jmgc/swift,aschwaighofer/swift,xwu/swift,hooman/swift,nathawes/swift,apple/swift,tkremenek/swift,atrick/swift,airspeedswift/swift,benlangmuir/swift,benlangmuir/swift,xwu/swift,benlangmuir/swift,allevato/swift,ahoppen/swift