When calling PrototypeHelper::remote_function(), the options hash may contain keys :success and :failure, which allow the caller to specify, respectively, onSuccess() and onFailure() JavaScript callbacks for the Ajax.updater() object. My patch adds the symbol :exception to this list so that the caller may specify an onException() JavaScript callback. This is necessary so that if the Ajax transport throws an exception it may be handled gracefully.
This is an extremely well defined, not-even-one-line addition, so I haven't included a test case. Without this patch, it is not possible to respond to exception-based Ajax errors (such as the server going down).
