Merge pull request #4089 from apple/underscore-playgroundquicklook

Begin moving PlaygroundQuickLook support to PlaygroundSupport module

Author: Dave Abrahams

stdlib/public/SDK/Foundation/Notification.swift

@@ -70,8 +70,8 @@ public struct Notification : ReferenceConvertible, Equatable, Hashable {
         } else if rhs.object != nil {
             return false
         }
-        if let lhsUserInfo = lhs.userInfo {
-            if let rhsUserInfo = rhs.userInfo {
+        if lhs.userInfo != nil {
+            if rhs.userInfo != nil {
                 // user info must be compared in the object form since the userInfo in swift is not comparable
                 return lhs._bridgeToObjectiveC() == rhs._bridgeToObjectiveC()
             } else {

stdlib/public/core/Mirror.swift

@@ -944,3 +944,7 @@ extension Mirror : CustomReflectable {
 
 @available(*, unavailable, renamed: "MirrorPath")
 public typealias MirrorPathType = MirrorPath
+
+// Staging so we can move the official declarations into PlaygroundSupport
+public typealias _CustomPlaygroundQuickLookable = CustomPlaygroundQuickLookable
+public typealias _PlaygroundQuickLook = PlaygroundQuickLook