fix(http): error on non-200 status codes

BREAKING CHANGE:

previously http would only error on network errors to match the fetch
specification. Now status codes less than 200 and greater than 299 will
cause Http's Observable to error.

Closes #5130.

modules/angular2/src/http/http_utils.ts

@@ -1,6 +1,7 @@
 import {isString} from 'angular2/src/facade/lang';
 import {RequestMethods} from './enums';
 import {makeTypeError} from 'angular2/src/facade/exceptions';
+import {Response} from './static_response';
 
 export function normalizeMethodName(method): RequestMethods {
   if (isString(method)) {
@@ -14,4 +15,6 @@ export function normalizeMethodName(method): RequestMethods {
   return method;
 }
 
+export const isSuccess = (status: number): boolean => (status >= 200 && status < 300);
+
 export {isJsObject} from 'angular2/src/facade/lang';