XCTest Overlay: Add XCTAssertThrowsError assertion
XCTest Overlay: Add XCTAssertThrowsError assertion

Add an assertion that can be used to check that an expression throws an
error, and if it does to run a block against that error which may
contain further checks.

Addresses rdar://problem/23789904.

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