gstreamer/plugin_feature: Make load downcast to Self
The loaded plugin feature is always of the same type as the unloaded
one. Move fn load to PluginFeatureExtManual to implement this.
Edited by Jan Alexander Steffens
Due to an influx of spam, we have had to impose restrictions on new accounts. Please see this wiki page for instructions on how to get full permissions. Sorry for the inconvenience.
The loaded plugin feature is always of the same type as the unloaded
one. Move fn load to PluginFeatureExtManual to implement this.