allow to pass data to error_callback

I had a need to pass extra information to the error callback. I think this can be useful.

```javascript
function custom_error(data){
    alert('Custom error of my_function. user = ' + data['user']);
}

Dajaxice.simple.my_function(
    callback, 
    {'user': 'tom'}, 
    {'error_callback': custom_error, 'error_callback_argv' :{'user' : 'tom'}}
);
```