6.7 Destructors/release actions

We've so far ignored the issue of what should happen when the user of a Haskell COM component finally signals that it is through with using the component. Here's a sketch of how support for it can be added:

• When the reference count for a component drops down to zero in the above implementation of release, the action releaseObj is called.
• The (library operation) releaseObj can as part of its clean up, call an component-specific release operation. Since the implementation of release is shared across all Haskell COM components, this has to be setup by storing a reference to it in the interface header.
• The component-specific release operation could invoke a user-supplied release action by requiring that the user-supplied module that implements the component export an action release.

ToDo:The above setup will create a reference count per-interface, and not per-component instance. We probably want to go for the latter, so this should be fixed ASAP.