chore(build): enable type-checking for TypeScript ES6 emit.

This requires delicate handling of type definitions which collide, because
we use TypeScript-provided lib.d.ts for --target=es5 and lib.es6.d.ts for
--target=es6.
We need to include our polyfill typings only in the --target=es5 case,
and the usages have to be consistent with lib.es6.d.ts.
Also starting with this change we now typecheck additional modules,
so this fixes a bunch of wrong typings which were never checked before.

Fixes #3178

modules/angular2/src/test_lib/e2e_util.ts

@@ -2,7 +2,7 @@
 /// <reference path="../../typings/angular-protractor/angular-protractor.d.ts" />
 /// <reference path="../../typings/jasmine/jasmine"/>
 
-import webdriver = require('selenium-webdriver');
+import * as webdriver from 'selenium-webdriver';
 
 export var browser: protractor.IBrowser = global['browser'];
 export var $: cssSelectorHelper = global['$'];