Implemented RegFlushKey and NtFlushKey.

diff --git a/server/protocol.def b/server/protocol.def
index f6e40eb..f838478 100644
--- a/server/protocol.def
+++ b/server/protocol.def
@@ -1295,6 +1295,12 @@
 @END
 
 
+/* Flush a registry key */
+@REQ(flush_key)
+    obj_handle_t hkey;         /* handle to the key */
+@END
+
+
 /* Enumerate registry subkeys */
 @REQ(enum_key)
     obj_handle_t hkey;         /* handle to registry key */