Define "requestsCount" var and "requests" hash unconditionally

[unclecheese]

There are situations in which global.document can be defined after the file is loaded, but before a request is created. This kills Request.prototype.create here:

  if (global.document) {
    this.index = Request.requestsCount++;
    Request.requests[this.index] = this;
  }

As the global exists, but those static properties were never defined. Is there any harm in defining them unconditionally?

[darrachequesne]

@unclecheese thanks!