This function will
be called when the request fails due to a network or server error, the url
is invalid, etc. It will also be called if the load or handle callback throws an
exception, unless djConfig.debugAtAllCosts is true. This allows deployed applications
to continue to run even when a logic error happens in the callback, while making
it easier to troubleshoot while in debug mode.
Set this explicitly to false to prevent publishing of topics related to
IO operations. Otherwise, if djConfig.ioPublish is set to true, topics
will be published via dojo.publish for different phases of an IO operation.
See dojo.__IoPublish for a list of topics that are published.
Default is false. If true, then a
"dojo.preventCache" parameter is sent in the request
with a value that changes with each request
(timestamp). Useful only with GET-type requests.