Creates a Drupal Ajax 'insert/prepend' command.
The 'insert/prepend' command instructs the client to use jQuery's prepend() method to prepend the given HTML content to the inside each element matched by the given selector.
This command is implemented by Drupal.AjaxCommands.prototype.insert() defined in misc/ajax.js.
$selector: A jQuery selector string. If the command is a response to a request from an #ajax form element then this value can be NULL.
$html: The data to use with the jQuery prepend() method.
$settings: An optional array of settings that will be used for this command only.
An array suitable for use with the ajax_render() function.
http://docs.jquery.com/Manipulation/prepend#content
function ajax_command_prepend($selector, $html, $settings = NULL) {
return array(
'command' => 'insert',
'method' => 'prepend',
'selector' => $selector,
'data' => $html,
'settings' => $settings,
);
}