mbostock/d3 — pull request #1261 by mrcarlosrendon (2013-05-20 23:14:19+00:00)
Title: Fix issue #1260

Fixes race condition that exists where the xhr.onload fires before
xhr.response has had a change to be set. This causes d3_json for example
to not get called.

The approach is to add another argument to the d3.xhr constructor. This method can then call xhr.response([the new callback]).