Fix for SR-3634: Error while accessing Locale.availableIdentifiers

Author: mamabusi

Foundation/NSLocale.swift

@@ -97,7 +97,7 @@ extension NSLocale {
     open class var availableLocaleIdentifiers: [String] {
         var identifiers = Array<String>()
         for obj in CFLocaleCopyAvailableLocaleIdentifiers()._nsObject {
-            identifiers.append((obj as! NSString)._swiftObject)
+            identifiers.append(obj as! String)
         }
         return identifiers
     }

TestFoundation/TestNSLocale.swift

@@ -20,7 +20,8 @@ class TestNSLocale : XCTestCase {
         return [
             ("test_constants", test_constants),
             ("test_Identifier", test_Identifier),
-            ("test_copy", test_copy)
+            ("test_copy", test_copy),
+            ("test_availableIdentifiers", test_availableIdentifiers),
         ]
     }
 
@@ -107,4 +108,8 @@ class TestNSLocale : XCTestCase {
 
         XCTAssertTrue(locale == localeCopy)
     }
+
+     func test_availableIdentifiers() {
+        XCTAssertNoThrow(Locale.availableIdentifiers)
+    }
 }