[stdlib] Add missing comment.
[stdlib] Add missing comment.

Swift SVN r29718

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