server: Redesign the server shutdown processing.

System processes are now killed only after the server persistence
delay has expired. New processes are not allowed to start during
shutdown.
diff --git a/server/trace.c b/server/trace.c
index 47e059e..8a11066 100644
--- a/server/trace.c
+++ b/server/trace.c
@@ -4546,6 +4546,7 @@
     { "SECTION_TOO_BIG",             STATUS_SECTION_TOO_BIG },
     { "SEMAPHORE_LIMIT_EXCEEDED",    STATUS_SEMAPHORE_LIMIT_EXCEEDED },
     { "SHARING_VIOLATION",           STATUS_SHARING_VIOLATION },
+    { "SHUTDOWN_IN_PROGRESS",        STATUS_SHUTDOWN_IN_PROGRESS },
     { "SUSPEND_COUNT_EXCEEDED",      STATUS_SUSPEND_COUNT_EXCEEDED },
     { "THREAD_IS_TERMINATING",       STATUS_THREAD_IS_TERMINATING },
     { "TIMEOUT",                     STATUS_TIMEOUT },