feat(http): add support for JSONP requests

Closes #2905
Closes #2818

modules/angular2/src/facade/lang.dart

@@ -190,6 +190,10 @@ class BaseException extends Error {
   }
 }
 
+Error makeTypeError([String message = ""]) {
+  return new BaseException(message);
+}
+
 const _NAN_KEY = const Object();
 
 // Dart can have identical(str1, str2) == false while str1 == str2

modules/angular2/src/facade/lang.ts

@@ -15,6 +15,10 @@ export class BaseException extends Error {
   toString(): string { return this.message; }
 }
 
+export function makeTypeError(message?: string): Error {
+  return new TypeError(message);
+}
+
 export var Math = _global.Math;
 export var Date = _global.Date;