Arena level interfaces need seperate refcounts

[Former user]

Currently, the process of providing an interface at the arena level is very different from providing an interface at the global level. This is due to the fact that all refencere counts on the interface are global. So a module doesn't know if its interface is still being used in a specific arena.

The interface head should be extended to include the ability to have a refcount for each arena that the interface is registered in.