srv_release_threads(): Actually wait for the threads to resume
from suspension. On CentOS 5 and possibly other platforms,
os_event_set() may be lost.

srv_resume_thread(): A counterpart of srv_suspend_thread().
Optionally wait for the event to be set, optionally with a timeout,
and then release the thread from suspension.

srv_free_slot(): Unconditionally suspend the thread. It is always
in resumed state when this function is entered.

srv_active_wake_master_thread_low(): Only call os_event_set().

srv_purge_coordinator_suspend(): Use srv_resume_thread() instead
of the complicated logic.