patch 9.0.0315: shell command is displayed in message window

Problem:    Shell command is displayed in message window.
Solution:   Do not echo the shell command in the message window.
diff --git a/src/ex_cmds.c b/src/ex_cmds.c
index 01518ff..9630252 100644
--- a/src/ex_cmds.c
+++ b/src/ex_cmds.c
@@ -1011,6 +1011,7 @@
     if (addr_count == 0)		// :!
     {
 	// echo the command
+	dont_use_message_window();
 	msg_start();
 	msg_putchar(':');
 	msg_putchar('!');