Creates a Drupal Ajax 'alert' command.
The 'alert' command instructs the client to display a JavaScript alert dialog box.
This command is implemented by Drupal.ajax.prototype.commands.alert() defined in misc/ajax.js.
$text: The message string to display to the user.
An array suitable for use with the ajax_render() function.
function ajax_command_alert($text) {
return array(
'command' => 'alert',
'text' => $text,
);
}