xhr RequestError breaks back-compat

[Adam Peller]

Prior to Dojo 1.8, xhr would throw an Error on xhr failure as so:

                        var err = new Error("Unable to load " + dfd.ioArgs.url \
+ " status:" + xhr.status);
                        err.status = xhr.status;
                        err.responseText = xhr.responseText;
                        err.xhr = xhr;
                        dfd.errback(err);

In 1.8, a RequestError? object is thrown with only message and response. The response object then has the status information.

It may not be reasonable to expect full back-compat (e.g. the exception type change, and perhaps passing back the xhr object would be a problem) but it's important to keep the status code in the same place, since that's often critical to how errors are handled, and prior to 1.8, that was the only way to reliably get that information.

[Bryan Forbes]

In [29708]:

Added back-compat properties to errors. refs #16023 !strict

[Bryan Forbes]

In [29709]:

Added back-compat properties to errors (1.8 backport). refs #16023 !strict

[Bryan Forbes]

I changed the back-compat layer for XHR to add those properties to the error.