Store jqXHR in promise object.

[maliming]

Resolve #8139

var req = abp.ajax({
  type: 'GET',
  url: '/api/identity/users'
});

req.then(function(result){
  console.log(result);
});

req.jqXHR.abort();

req.then() will create a new Deferred which will lost jqXHR. Must be saving return value first.

var req = abp.ajax({
  type: 'GET',
  url: '/api/identity/users'
}).then(function(result){
  console.log(result);
});

//Not working.
req.jqXHR.abort();