Added a close_handle method to the object operations, and use it to
implement registry notifications and the strange behavior of
CloseHandle on winstation/desktop handles.

diff --git a/server/signal.c b/server/signal.c
index f3b0f5f..9ce3640 100644
--- a/server/signal.c
+++ b/server/signal.c
@@ -64,6 +64,7 @@
     NULL,                     /* satisfied */
     no_signal,                /* signal */
     no_get_fd,                /* get_fd */
+    no_close_handle,          /* close_handle */
     handler_destroy           /* destroy */
 };