Revert PTHREAD_MUTEX_INITIALIZER to PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP
since that is actually closer to what linux does.
* thread.h (cw_cancel_action): New enum.
(cancelable_wait): Use cw_cancel_action as third argument.
* thread.cc (cancelable_wait): Ditto. Don't wait for cancel if cancel_action
== cw_no_cancel.
(pthread::create): Don't wait for cancel event since that is racy.
(pthread_mutex::pthread_mutex): Set default to PTHREAD_MUTEX_ERRORCHECK.
(pthread_mutexattr::pthread_mutexattr): Ditto.
(pthread_mutex::_lock): Tell cancelable_wait not to wait for cancellation
event.
(semaphore::_timedwait): Accommodate change in cancelable_wait args.
(pthread::join): Ditto.
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