they become candidates for reuse. Without this fix, some of the
state from a thread structure's previous incarnation could interfere
with its new one. Specifically, a non-bound thread started as
"suspended" (see pthread_attr_setcreatesuspend_np()) might not get
scheduled at all when resumed, as the "active" flag would be set
spuriously.
Reviewed by: deischen@, davidxu@
MFC after: 1 week
977e36e94a