Scheduler Activation types were removed in NetBSD 5.0. Old type set is not
matching the new world POSIX threads library.
Only TD_STATE_RUNNING, TD_STATE_ZOMBIE are still applicable - keep it.
Keep TD_STATE_UNKNOWN as generic unrecognized type.
Add new TD_STATE_DEAD one. The TD_STATE_DEAD type is represented by number
6 in the POSIX threads library, but for the sake of compatibility with
older software using pthread_dbg - renumber it to 7, as six was reserved
for TD_STATE_SUSPENDED.
Old removed state types are marked as reserved and unused.
Sponsored by <The NetBSD Foundation>