The interoperability system now runs after all mods are loaded. This
prevents the `opt_depends` table getting too long and also makes
supporting mods easier for server owners because they can simply drop
their i14y files into the interoperability directory without needing to
change the mod files.

See API documentation for details on interoperability and how the
loading mechanism works and what additional i14y options the API offers.

Might also be relevant for !5