CallHook() method is called from that place.
Registering your plugin is done by providing a
-/usr/lib/gforge/plugins/<pluginname>/include/<pluginname>-init.php.
+/usr/share/gforge/plugins/<pluginname>/include/<pluginname>-init.php.
It will be parsed by the PluginManager object. That file should
contain a call to register_plugin(), passing it an object of the
appropriate class. See the helloworld plugin for an example.