gst/gstregistrybinary.c: If an element supports the Uri interface, returns a valid...

gst/gstregistrybinary.c: If an element supports the Uri interface, returns a valid pointer to the supported URI proto...

Original commit message from CVS:
* gst/gstregistrybinary.c: (gst_registry_binary_save_feature),
(gst_registry_binary_load_feature),
(gst_registry_binary_load_plugin):
If an element supports the Uri interface, returns a valid pointer
to the supported URI protocols but this pointer contains nothing
don't try to save that as it will corrupt the registry.
Don't unref the plugin if we added it to the registry already but
fail to load a feature as gst_registry_add_plugin() takes ownership
of the plugin.
Improve debugging a bit.