Workaround for microsoft#1168 in TS 1.5

Author: alexeagle

bin/lib.d.ts

@@ -876,19 +876,12 @@ interface RegExpConstructor {
 
 declare var RegExp: RegExpConstructor;
 
-interface Error {
+declare class Error {
     name: string;
     message: string;
+    constructor(message?: string);
 }
 
-interface ErrorConstructor {
-    new (message?: string): Error;
-    (message?: string): Error;
-    prototype: Error;
-}
-
-declare var Error: ErrorConstructor;
-
 interface EvalError extends Error {
 }