Make the event module to accept two event types, and pass around the event
context. Use bytes-based events to trigger tcache GC on deallocation, and get
rid of the tcache ticker.
Fold the tsd_state check onto the event threshold check. The fast threshold is
set to 0 when tsd switch to non-nominal.
The fast_threshold can be reset by remote threads, to refect the non nominal tsd
state change.
