Clarify equivalence between SequenceType.forEach and for-in loops in doc comment
Clarify equivalence between SequenceType.forEach and for-in loops in doc comment

No functional change.

Swift SVN r30375

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