Make "true" and "false" Boolean literal constants for the BooleanLiteralConvertible protocol.

Introduce the new BooleanLiteralConvertible protocol for Boolean
literals. Take "true" and "false" as real keywords (which is most of the
reason for the testsuite churn). Make Bool BooleanLiteralConvertible
and the default Boolean literal type, and ObjCBool
BooleanLiteralConvertible. Fixes <rdar://problem/17405310> and the
recent regression that made ObjCBool not work with true/false.


Swift SVN r19728

stdlib/objc/Foundation/NSStringAPI.swift

@@ -500,7 +500,7 @@ extension String {
       var stop_ = false
       body(line: line!, stop: &stop_)
       if stop_ {
-        UnsafePointer<ObjCBool>(stop).memory = ObjCBool(true)
+        UnsafePointer<ObjCBool>(stop).memory = true
       }
     }
   }