add one more option `jsonp` for $.ajax.

### new features
add two features for af.

#### 1. user don't want to add callback=? to the url which is very inconvenient and unnecessary.
```
$.ajax({
  url: 'http:/example.com/group/swRightHP/do_query.jsonp?firstCatId=7&secCatId=727&leafCatId=1',
  type: 'get',
  data: {a: 1, b: 2},
  dataType: 'jsonp',
  success: function(data) {
       console.log(data);
   },
   error: function() {
       console.err(arguments);
   }
})
```
requested url: 
**http:/example.com/group/swRightHP/do_query.jsonp?firstCatId=7&secCatId=727&leafCatId=1&callback=jsonp_callback1**

#### 2. add one more option jsonp for $.ajax, so we can specify the name of the callback now.
```
$.ajax({
  url: 'http:/example.com/group/swRightHP/do_query.jsonp?firstCatId=7&secCatId=727&leafCatId=1',
  type: 'get',
  data: {a: 1, b: 2},
  dataType: 'jsonp',
  jsonp: 'myCallback',
  success: function(data) {
       console.log(data);
   },
   error: function() {
       console.err(arguments);
   }
})
```
-> requested url: **http:/example.com/group/swRightHP/do_query.jsonp?firstCatId=7&secCatId=727&leafCatId=1&myCallback=jsonp_callback1**

See also: http://api.jquery.com/jquery.ajax/
Merge pull request #505 from LeoYuan/patch-3

add one more option `jsonp` for $.ajax.