patch 8.2.1281: the "trailing characters" error can be hard to understand

Problem:    The "trailing characters" error can be hard to understand.
Solution:   Add the trailing characters to the message.
diff --git a/src/ex_cmds.c b/src/ex_cmds.c
index 59c562b..e8e38aa 100644
--- a/src/ex_cmds.c
+++ b/src/ex_cmds.c
@@ -3816,7 +3816,7 @@
 	eap->nextcmd = check_nextcmd(cmd);
 	if (eap->nextcmd == NULL)
 	{
-	    emsg(_(e_trailing));
+	    semsg(_(e_trailing_arg), cmd);
 	    return;
 	}
     }