Various updates including:

• Update the tasks to push Giant down into the various compat ABIs (really sync up the MPSAFE flags) as done.
• Update the task to add witness checks on thread exit as done.
• Update the atomic_fetchadd() and refcount API tasks as done.
• Add a new WIP task describing the intr_event stuff.
• Discard some poorly thought not started tasks (or ones OBE).