Async: Check on responseText always fails if a local resource is requested and XHR's responseType is set

[Sasha Go]

In recent versions of Chrome and Firefox the following code always calls errback if 'whatever' is a local resource

var xhr = getXMLHttpRequest();
xhr.open('GET', 'whatever');
xhr.responseType = 'arraybuffer';
sendXMLHttpRequest(xhr);

Here we need xhr.response, not xhr.responseText or xhr.responseXML, but MochiKit.Async._xhr_onreadystatechange fails if status is 0 and responseText is not set.

[Per Cederberg]

Could you hack up a patch for this and add a pull request?

[Per Cederberg]

Thanks for the patch! Now merged and repacked.