(MSLEEP_MUTEX): New define for third parameter to msleep_event_name.
(MSLEEP_SEM): Ditto.
(MSLEEP_EVENT): Ditto.
(msleep_event_name): Add third parameter to allow multiple
synchronization objects per ident.
(_msleep): Implement new synchronization technique to make sure
that all threads have been woken up by a corresponding wakeup call.
(wakeup): Ditto.