Implemented the SMTO_ABORTIFHUNG flag of SendMessageTimeout.

diff --git a/server/protocol.def b/server/protocol.def
index f01e1dc..6a8c460 100644
--- a/server/protocol.def
+++ b/server/protocol.def
@@ -1564,6 +1564,7 @@
 @REQ(send_message)
     thread_id_t     id;        /* thread id */
     int             type;      /* message type (see below) */
+    int             flags;     /* message flags (see below) */
     user_handle_t   win;       /* window handle */
     unsigned int    msg;       /* message code */
     unsigned int    wparam;    /* parameters */
@@ -1586,6 +1587,7 @@
     MSG_POSTED,         /* posted message (from PostMessageW), always Unicode */
     MSG_HARDWARE        /* hardware message */
 };
+#define SEND_MSG_ABORT_IF_HUNG  0x01
 
 
 /* Get a message from the current queue */