[stdlib] Separate Sequence type for enumerate
[stdlib] Separate Sequence type for enumerate

Avoids surprise in case someone makes a generator with reference
semantics

Swift SVN r21886

tjw/swift,jopamer/swift,bitjammer/swift,KrishMunot/swift,swiftix/swift,apple/swift,milseman/swift,OscarSwanros/swift,jtbandes/swift,swiftix/swift.old,dreamsxin/swift,kentya6/swift,lorentey/swift,modocache/swift,hooman/swift,roambotics/swift,ken0nek/swift,ken0nek/swift,jckarter/swift,slavapestov/swift,kentya6/swift,jmgc/swift,therealbnut/swift,jopamer/swift,Jnosh/swift,ken0nek/swift,CodaFi/swift,hooman/swift,gottesmm/swift,swiftix/swift.old,tardieu/swift,jmgc/swift,SwiftAndroid/swift,alblue/swift,cbrentharris/swift,xwu/swift,ahoppen/swift,airspeedswift/swift,devincoughlin/swift,shajrawi/swift,bitjammer/swift,djwbrown/swift,practicalswift/swift,manavgabhawala/swift,parkera/swift,modocache/swift,IngmarStein/swift,lorentey/swift,natecook1000/swift,tjw/swift,rudkx/swift,OscarSwanros/swift,benlangmuir/swift,jmgc/swift,Ivacker/swift,gribozavr/swift,practicalswift/swift,huonw/swift,KrishMunot/swift,shahmishal/swift,jopamer/swift,austinzheng/swift,parkera/swift,shahmishal/swift,danielmartin/swift,modocache/swift,practicalswift/swift,khizkhiz/swift,lorentey/swift,Ivacker/swift,tjw/swift,jtbandes/swift,glessard/swift,allevato/swift,LeoShimonaka/swift,gribozavr/swift,milseman/swift,swiftix/swift.old,austinzheng/swift,gregomni/swift,JaSpa/swift,bitjammer/swift,huonw/swift,Jnosh/swift,johnno1962d/swift,sschiau/swift,sdulal/swift,gmilos/swift,kperryua/swift,ben-ng/swift,return/swift,dduan/swift,CodaFi/swift,stephentyrone/swift,SwiftAndroid/swift,deyton/swift,kperryua/swift,kentya6/swift,atrick/swift,sdulal/swift,sschiau/swift,sdulal/swift,djwbrown/swift,manavgabhawala/swift,nathawes/swift,adrfer/swift,gribozavr/swift,SwiftAndroid/swift,harlanhaskins/swift,sschiau/swift,MukeshKumarS/Swift,MukeshKumarS/Swift,Jnosh/swift,xedin/swift,djwbrown/swift,natecook1000/swift,JaSpa/swift,nathawes/swift,kperryua/swift,kusl/swift,JGiola/swift,codestergit/swift,deyton/swift,codestergit/swift,johnno1962d/swift,return/swift,manavgabhawala/swift,jckarter/swift,hughbe/swift,calebd/swift,codestergit/swift,harlanhaskins/swift,nathawes/swift,djwbrown/swift,allevato/swift,huonw/swift,manavgabhawala/swift,gribozavr/swift,KrishMunot/swift,arvedviehweger/swift,therealbnut/swift,gmilos/swift,adrfer/swift,arvedviehweger/swift,uasys/swift,sschiau/swift,cbrentharris/swift,gmilos/swift,frootloops/swift,khizkhiz/swift,aschwaighofer/swift,swiftix/swift,tardieu/swift,huonw/swift,zisko/swift,manavgabhawala/swift,huonw/swift,danielmartin/swift,hooman/swift,ben-ng/swift,xwu/swift,jtbandes/swift,huonw/swift,Jnosh/swift,tinysun212/swift-windows,gmilos/swift,zisko/swift,therealbnut/swift,djwbrown/swift,nathawes/swift,karwa/swift,uasys/swift,hooman/swift,gregomni/swift,KrishMunot/swift,bitjammer/swift,natecook1000/swift,modocache/swift,aschwaighofer/swift,brentdax/swift,jckarter/swift,kentya6/swift,stephentyrone/swift,amraboelela/swift,deyton/swift,dduan/swift,djwbrown/swift,sschiau/swift,practicalswift/swift,jmgc/swift,hughbe/swift,tkremenek/swift,mightydeveloper/swift,brentdax/swift,bitjammer/swift,jckarter/swift,sdulal/swift,kusl/swift,MukeshKumarS/Swift,parkera/swift,russbishop/swift,natecook1000/swift,johnno1962d/swift,slavapestov/swift,karwa/swift,uasys/swift,hughbe/swift,therealbnut/swift,LeoShimonaka/swift,austinzheng/swift,parkera/swift,kperryua/swift,airspeedswift/swift,kusl/swift,khizkhiz/swift,lorentey/swift,deyton/swift,lorentey/swift,alblue/swift,russbishop/swift,arvedviehweger/swift,tinysun212/swift-windows,hooman/swift,sdulal/swift,practicalswift/swift,frootloops/swift,tjw/swift,roambotics/swift,glessard/swift,shahmishal/swift,modocache/swift,arvedviehweger/swift,jmgc/swift,swiftix/swift,emilstahl/swift,LeoShimonaka/swift,atrick/swift,johnno1962d/swift,uasys/swift,LeoShimonaka/swift,felix91gr/swift,khizkhiz/swift,danielmartin/swift,tkremenek/swift,practicalswift/swift,brentdax/swift,austinzheng/swift,gribozavr/swift,CodaFi/swift,roambotics/swift,codestergit/swift,KrishMunot/swift,MukeshKumarS/Swift,return/swift,alblue/swift,glessard/swift,brentdax/swift,jopamer/swift,sdulal/swift,adrfer/swift,OscarSwanros/swift,Ivacker/swift,hooman/swift,adrfer/swift,slavapestov/swift,johnno1962d/swift,gottesmm/swift,rudkx/swift,shajrawi/swift,aschwaighofer/swift,hughbe/swift,swiftix/swift.old,harlanhaskins/swift,natecook1000/swift,tinysun212/swift-windows,ben-ng/swift,emilstahl/swift,nathawes/swift,nathawes/swift,airspeedswift/swift,kentya6/swift,arvedviehweger/swift,shahmishal/swift,xwu/swift,russbishop/swift,modocache/swift,sschiau/swift,adrfer/swift,atrick/swift,KrishMunot/swift,aschwaighofer/swift,xwu/swift,tkremenek/swift,aschwaighofer/swift,danielmartin/swift,jmgc/swift,devincoughlin/swift,gribozavr/swift,slavapestov/swift,allevato/swift,IngmarStein/swift,deyton/swift,felix91gr/swift,ken0nek/swift,kentya6/swift,alblue/swift,atrick/swift,therealbnut/swift,tardieu/swift,IngmarStein/swift,xedin/swift,allevato/swift,gottesmm/swift,russbishop/swift,swiftix/swift,practicalswift/swift,ben-ng/swift,calebd/swift,shajrawi/swift,amraboelela/swift,alblue/swift,gregomni/swift,danielmartin/swift,return/swift,xwu/swift,xwu/swift,shahmishal/swift,mightydeveloper/swift,JGiola/swift,stephentyrone/swift,MukeshKumarS/Swift,tkremenek/swift,Jnosh/swift,felix91gr/swift,djwbrown/swift,ken0nek/swift,cbrentharris/swift,kusl/swift,shajrawi/swift,arvedviehweger/swift,JaSpa/swift,tardieu/swift,modocache/swift,kstaring/swift,OscarSwanros/swift,benlangmuir/swift,jmgc/swift,apple/swift,tinysun212/swift-windows,ken0nek/swift,sdulal/swift,gottesmm/swift,JaSpa/swift,tinysun212/swift-windows,kstaring/swift,benlangmuir/swift,gmilos/swift,harlanhaskins/swift,lorentey/swift,frootloops/swift,swiftix/swift.old,gottesmm/swift,tjw/swift,calebd/swift,uasys/swift,parkera/swift,kstaring/swift,return/swift,rudkx/swift,cbrentharris/swift,dduan/swift,swiftix/swift.old,rudkx/swift,danielmartin/swift,tkremenek/swift,shajrawi/swift,arvedviehweger/swift,ahoppen/swift,kusl/swift,brentdax/swift,gmilos/swift,allevato/swift,jtbandes/swift,JGiola/swift,shahmishal/swift,JGiola/swift,uasys/swift,tinysun212/swift-windows,harlanhaskins/swift,Ivacker/swift,milseman/swift,milseman/swift,austinzheng/swift,zisko/swift,therealbnut/swift,khizkhiz/swift,khizkhiz/swift,shajrawi/swift,uasys/swift,devincoughlin/swift,LeoShimonaka/swift,austinzheng/swift,swiftix/swift.old,kstaring/swift,jopamer/swift,kperryua/swift,johnno1962d/swift,JGiola/swift,emilstahl/swift,devincoughlin/swift,airspeedswift/swift,CodaFi/swift,swiftix/swift,hughbe/swift,jckarter/swift,stephentyrone/swift,milseman/swift,emilstahl/swift,OscarSwanros/swift,KrishMunot/swift,stephentyrone/swift,jtbandes/swift,MukeshKumarS/Swift,karwa/swift,calebd/swift,amraboelela/swift,xedin/swift,russbishop/swift,shahmishal/swift,milseman/swift,gregomni/swift,CodaFi/swift,atrick/swift,deyton/swift,alblue/swift,tardieu/swift,aschwaighofer/swift,nathawes/swift,kusl/swift,felix91gr/swift,roambotics/swift,danielmartin/swift,kentya6/swift,apple/swift,sdulal/swift,karwa/swift,LeoShimonaka/swift,frootloops/swift,karwa/swift,hughbe/swift,SwiftAndroid/swift,calebd/swift,dreamsxin/swift,ben-ng/swift,Ivacker/swift,khizkhiz/swift,swiftix/swift,SwiftAndroid/swift,kentya6/swift,emilstahl/swift,gottesmm/swift,ben-ng/swift,cbrentharris/swift,codestergit/swift,natecook1000/swift,swiftix/swift,gregomni/swift,austinzheng/swift,jtbandes/swift,lorentey/swift,glessard/swift,mightydeveloper/swift,bitjammer/swift,roambotics/swift,cbrentharris/swift,swiftix/swift.old,felix91gr/swift,return/swift,emilstahl/swift,apple/swift,gribozavr/swift,milseman/swift,JaSpa/swift,hooman/swift,parkera/swift,shajrawi/swift,calebd/swift,manavgabhawala/swift,frootloops/swift,amraboelela/swift,roambotics/swift,xedin/swift,shajrawi/swift,CodaFi/swift,OscarSwanros/swift,jckarter/swift,mightydeveloper/swift,amraboelela/swift,codestergit/swift,slavapestov/swift,ahoppen/swift,glessard/swift,airspeedswift/swift,russbishop/swift,bitjammer/swift,tjw/swift,dduan/swift,practicalswift/swift,russbishop/swift,JaSpa/swift,calebd/swift,tkremenek/swift,devincoughlin/swift,johnno1962d/swift,airspeedswift/swift,xedin/swift,huonw/swift,OscarSwanros/swift,CodaFi/swift,kstaring/swift,Ivacker/swift,manavgabhawala/swift,benlangmuir/swift,xwu/swift,gregomni/swift,karwa/swift,jopamer/swift,frootloops/swift,atrick/swift,kstaring/swift,mightydeveloper/swift,cbrentharris/swift,apple/swift,stephentyrone/swift,ahoppen/swift,kperryua/swift,benlangmuir/swift,karwa/swift,gottesmm/swift,airspeedswift/swift,aschwaighofer/swift,slavapestov/swift,zisko/swift,rudkx/swift,brentdax/swift,gribozavr/swift,kstaring/swift,codestergit/swift,frootloops/swift,IngmarStein/swift,mightydeveloper/swift,jopamer/swift,adrfer/swift,amraboelela/swift,emilstahl/swift,sschiau/swift,tardieu/swift,Jnosh/swift,JaSpa/swift,jtbandes/swift,ahoppen/swift,kusl/swift,devincoughlin/swift,kusl/swift,glessard/swift,natecook1000/swift,LeoShimonaka/swift,emilstahl/swift,gmilos/swift,therealbnut/swift,parkera/swift,devincoughlin/swift,ken0nek/swift,amraboelela/swift,mightydeveloper/swift,Ivacker/swift,cbrentharris/swift,alblue/swift,mightydeveloper/swift,sschiau/swift,zisko/swift,tardieu/swift,tjw/swift,kperryua/swift,IngmarStein/swift,shahmishal/swift,dduan/swift,slavapestov/swift,return/swift,zisko/swift,brentdax/swift,dduan/swift,MukeshKumarS/Swift,rudkx/swift,tinysun212/swift-windows,ahoppen/swift,karwa/swift,felix91gr/swift,allevato/swift,hughbe/swift,SwiftAndroid/swift,IngmarStein/swift,benlangmuir/swift,parkera/swift,harlanhaskins/swift,Ivacker/swift,zisko/swift,lorentey/swift,xedin/swift,xedin/swift,adrfer/swift,jckarter/swift,SwiftAndroid/swift,apple/swift,stephentyrone/swift,deyton/swift,Jnosh/swift,devincoughlin/swift,xedin/swift,JGiola/swift,IngmarStein/swift,harlanhaskins/swift,tkremenek/swift,LeoShimonaka/swift,felix91gr/swift,allevato/swift,ben-ng/swift,dduan/swift