Change threadDictionary to NSMutableDictionary

Author: omochi

Foundation/Thread.swift

@@ -153,8 +153,8 @@ open class Thread : NSObject {
 #endif
     internal var _status = _NSThreadStatus.initialized
     internal var _cancelled = false
-    /// - Note: this differs from the Darwin implementation in that the keys must be Strings
-    open var threadDictionary = [String : Any]()
+    
+    open private(set) var threadDictionary: NSMutableDictionary = NSMutableDictionary()
 
     internal init(thread: pthread_t) {
         // Note: even on Darwin this is a non-optional pthread_t; this is only used for valid threads, which are never null pointers.

Foundation/XMLParser.swift

@@ -471,7 +471,7 @@ open class XMLParser : NSObject {
         if let p = parser {
             Thread.current.threadDictionary["__CurrentNSXMLParser"] = p
         } else {
-            Thread.current.threadDictionary.removeValue(forKey: "__CurrentNSXMLParser")
+            Thread.current.threadDictionary.removeObject(forKey: "__CurrentNSXMLParser")
         }
     }