Restore r15378: fix the AST printer to print "let" for let variables. Update the associated tests.
Restore r15378: fix the AST printer to print "let" for let variables.
Update the associated tests.

Swift SVN r15536

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