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/mutex.c b/server/mutex.c
index c1b59bb..c9bee83 100644
--- a/server/mutex.c
+++ b/server/mutex.c
@@ -56,6 +56,7 @@
     mutex_satisfied,           /* satisfied */
     mutex_signal,              /* signal */
     no_get_fd,                 /* get_fd */
+    no_close_handle,           /* close_handle */
     mutex_destroy              /* destroy */
 };