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_docmd.c b/src/ex_docmd.c
index 4f27898..bd3de8f 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -2396,7 +2396,7 @@
 	    && *ea.arg != '"' && (*ea.arg != '|' || (ea.argt & EX_TRLBAR) == 0))
     {
 	// no arguments allowed but there is something
-	errormsg = _(e_trailing);
+	errormsg = ex_errmsg(e_trailing_arg, ea.arg);
 	goto doend;
     }
 
@@ -7725,7 +7725,7 @@
     if (*eap->arg == NUL)		// No argument?
 	emsg(_(e_argreq));
     else if (eap->arg[1] != NUL)	// more than one character?
-	emsg(_(e_trailing));
+	semsg(_(e_trailing_arg), eap->arg);
     else
     {
 	pos = curwin->w_cursor;		// save curwin->w_cursor