score: Thread life cycle re-implementation

The thread deletion is now supported on SMP.

This change fixes the following PRs:

PR1814: SMP race condition between stack free and dispatch

PR2035: psxcancel reveals NULL pointer access in _Thread_queue_Extract()

The POSIX cleanup handler are now called in the right context (should be
called in the context of the terminating thread).

http://pubs.opengroup.org/onlinepubs/009695399/functions/xsh_chap02_09.html

Add a user extension the reflects a thread termination event.  This is
used to reclaim the Newlib reentrancy structure (may use file
operations), the POSIX cleanup handlers and the POSIX key destructors.

cpukit/libmisc/monitor/mon-prmisc.c

@@ -135,6 +135,8 @@ static const rtems_assoc_t rtems_monitor_state_assoc[] = {
     { "Wrwlk",  STATES_WAITING_FOR_RWLOCK, 0 },
     { "Wisig",  STATES_INTERRUPTIBLE_BY_SIGNAL, 0 },
     { "Wwkup",  STATES_WAITING_FOR_BSD_WAKEUP, 0 },
+    { "Wterm",  STATES_WAITING_FOR_TERMINATION, 0 },
+    { "ZOMBI",  STATES_ZOMBIE, 0 },
     { 0, 0, 0 },
 };