Ajax: Support an alternative completeCallback API for transports

Apart from the existing API:

```js
function( status, statusText, responses, headers ) {}
```
a new API is now available:
```js
function( { status, statusText, responses, headers } ) {}
```

This makes it possible to add new parameters in the future without relying on
their order among parameters and being able to provide them selectively.

Ref gh-4405

src/ajax.js

@@ -712,8 +712,19 @@ jQuery.extend( {
 
  // Callback for when everything is done
  function done( status, nativeStatusText, responses, headers ) {
- var isSuccess, success, error, response, modified,
- statusText = nativeStatusText;
+ var isSuccess, success, error, response, modified, statusText;
+
+ if ( typeof status === "object" ) {
+
+ // The new, object-based API
+ nativeStatusText = status.statusText;
+ responses = status.responses;
+ headers = status.headers;
+
+ status = status.status;
+ }
+
+ statusText = nativeStatusText;
 
  // Ignore repeat invocations
  if ( completed ) {

src/ajax/xhr.js

@@ -64,23 +64,23 @@ jQuery.ajaxTransport( function( options ) {
  if ( type === "abort" ) {
  xhr.abort();
  } else if ( type === "error" ) {
- complete(
+ complete( {
 
  // File: protocol always yields status 0; see #8605, #14207
- xhr.status,
- xhr.statusText
- );
+ status: xhr.status,
+ statusText: xhr.statusText
+ } );
  } else {
- complete(
- xhrSuccessStatus[ xhr.status ] || xhr.status,
- xhr.statusText,
+ complete( {
+ status: xhrSuccessStatus[ xhr.status ] || xhr.status,
+ statusText: xhr.statusText,
 
  // For XHR2 non-text, let the caller handle it (gh-2498)
- ( xhr.responseType || "text" ) === "text" ?
+ responses: ( xhr.responseType || "text" ) === "text" ?
  { text: xhr.responseText } :
  { binary: xhr.response },
- xhr.getAllResponseHeaders()
- );
+ headers: xhr.getAllResponseHeaders()
+ } );
  }
  }
  };