chore(build): update TypeScript version to unreleased beta

Also fixup the typings which were broken by changes in typescript's lib.d.ts.
Second attempt to merge this, now that bugfix for tsd is in.

modules/angular2/src/facade/math.ts

@@ -6,4 +6,4 @@ import {global} from 'angular2/src/facade/lang';
 export var __esModule = true;
 
 export var Math = global.Math;
-export var NaN = global.NaN;
+export var NaN = typeof NaN;