"external types" for d.ts files dependent on others #1402

interface JSZipObject {
  name: string;
  dir: boolean;
  date: Date;
  comment: string;
  options: JSZipObjectOptions;

  asText(): string;
  asBinary(): string;
  asArrayBuffer(): ArrayBuffer;
  asUint8Array(): Uint8Array;
  //asNodeBuffer(): Buffer; <-- Disabled to prevent node.d.ts dependency
}

// jszip.d.ts
/// <reference path="../node/node.d.ts" />
external interface Buffer: "../node/node.d.ts";

// use.d.ts
/// <referernce path="jszip.d.ts" />
var zip: JSZipObject;
var text = zip.asText(); // works fine without node.d.ts

var buffer = zip.asNodeBuffer(); // typeof any when there is no node.d.ts;
// No error but a warning: "interface Buffer should be defined by "node.d.ts"

// bar.d.ts
/// <reference path="foo.d.ts" />;
external class Foo: "foo.d.ts"; // This should not block Foo definition by foo.d.ts
interface Bar {
  foo: Foo;
}