set_loaded_plugins
Description:
Sets the list of loaded plugins for this.
When this function is called, the Engine will load all the plugins whose names are in 
      plugin_names, and ensures all other active plugins are unloaded.
If plugin_names is null, all plugins will be unloaded.
Parameters:
| this | A Engine. | 
| plugin_names | A null-terminated array of plugin names, or null. |