[NSThread] Updated to match Darwin version (swiftlang#440)

* Updated to match Darwin version

* Fixed other occurence of Thread.current

Author: damuellen

Foundation/NSThread.swift

@@ -59,7 +59,7 @@ private func NSThreadStart(_ context: UnsafeMutablePointer<Void>?) -> UnsafeMuta
 public class Thread: NSObject {
 
     static internal var _currentThread = NSThreadSpecific<Thread>()
-    public static func current() -> Thread {
+    public static var current: Thread {
         return Thread._currentThread.get() {
             return Thread(thread: pthread_self())
         }

Foundation/NSXMLParser.swift

@@ -460,7 +460,7 @@ public class XMLParser : NSObject {
     public var allowedExternalEntityURLs: Set<URL>?
 
     internal static func currentParser() -> XMLParser? {
-        if let current = Thread.current().threadDictionary["__CurrentNSXMLParser"] {
+        if let current = Thread.current.threadDictionary["__CurrentNSXMLParser"] {
             return current as? XMLParser
         } else {
             return nil
@@ -469,9 +469,9 @@ public class XMLParser : NSObject {
 
     internal static func setCurrentParser(_ parser: XMLParser?) {
         if let p = parser {
-            Thread.current().threadDictionary["__CurrentNSXMLParser"] = p
+            Thread.current.threadDictionary["__CurrentNSXMLParser"] = p
         } else {
-            Thread.current().threadDictionary.removeValue(forKey: "__CurrentNSXMLParser")
+            Thread.current.threadDictionary.removeValue(forKey: "__CurrentNSXMLParser")
         }
     }
 

TestFoundation/TestNSThread.swift

@@ -26,8 +26,8 @@ class TestNSThread : XCTestCase {
     }
 
     func test_currentThread() {
-        let thread1 = Thread.current()
-        let thread2 = Thread.current()
+        let thread1 = Thread.current
+        let thread2 = Thread.current
         XCTAssertNotNil(thread1)
         XCTAssertNotNil(thread2)
         XCTAssertEqual(thread1, thread2)