[DocComment] Add test for bogus image URLs and enable all tests
[DocComment] Add test for bogus image URLs and enable all tests

- Reenable doc comment extension tests by moving the inputs into the
  Inputs subdirectory. rdar://problem/21295424

- cmark could crash when getting an empty URL in an image element,
  because the URL was stored as a raw char * pointer. This was fixed in
  jgm/cmark pull request https://github.com/jgm/cmark/pull/38, so GitHub/master
  is pulled into our cmark clone.
  rdar://problem/21910368

Swift SVN r30475

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