Fix #14683 - AJAX: Invalid url triggers networkerror in Chrome


Fixed the issues mentioned in http://bugs.jquery.com/ticket/14683

When an invalid url is used in an ajax request no callback are called. You can see the issue here http://jsfiddle.net/4FxSt/.

```fail``` and ```always``` callbacks will not be called in the example below

```
//pulled from ticket
$.get('//example.com:80q').then(function () {
    console.log('not called'); 
}).fail(function () {
    console.log('not called'); 
}).always(function () {
    console.log('not called');
});
```

This appears because of the added onerror listener to xhr at https://github.com/jquery/jquery/blob/master/src/ajax/xhr.js#L110

Because this successfully fires (in chrome and safari) when trying an invalid url the try catch at https://github.com/jquery/jquery/blob/master/src/ajax.js#L649 throws an error instead of calling done() when chrome triggers a networkerror. Unfortunately throwing this error prevents the deferred callback from being called.

This can be fixed by delaying throwing the error by adding a setTimeout around throw e.

The alternative fix for this issue would be to remove the ```xhr.onerror``` callback that is not consistently being called with all browsers or remove ```throw e``` line.