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/tsd.json

@@ -15,7 +15,7 @@
       "commit": "055b3172e8eb374a75826710c4d08677872620d3"
     },
     "node/node.d.ts": {
-      "commit": "d5f92f93bdb49f332fa662ff1d0cc8700f02e4dc"
+      "commit": "51738fdf1643d269067861b405e87503b7479236"
     },
     "rx/rx.d.ts": {
       "commit": "3882d337bb0808cde9fe4c08012508a48c135482"