shop credit feedback (trunk only)

Fix the first of a couple of minor things I noticed when viewing
that guy's ttyrec about a hidden inventory item which turned out to be
scrolls of scare monster on the used-up items section of his shop bill.

     Be more precise when a shopkeeper gives the hero credit for dropped
gold.  Instead of just displaying
  N zorkmids are added to your credit.
show either
  You have established N zorkmids credit.
when you had no previous credit, or
  N zorkmids added to your credit; total is now X zorkmids.
when adding to existing credit.

src/shk.c

@@ -2722,11 +2722,16 @@ xchar x, y;
 			eshkp->loan = 0L;
 			Your("debt is paid off.");
 		    }
-		    pline("%ld %s %s added to your credit.",
+		    if (eshkp->credit == delta)
-				delta, currency(delta), delta > 1L ? "are" : "is");
+			You("have established %ld %s credit.",
+			    delta, currency(delta));
+		    else
+			pline("%ld %s added to your credit; total is now %ld %s.",
+			      delta, currency(delta),
+			      eshkp->credit, currency(eshkp->credit));
 		}
-		if(offer) goto move_on;
+
-		else {
+		if (!offer) {
 		    if(!isgold) {
 			if (container)
 			    dropped_container(obj, shkp, FALSE);
@@ -2736,7 +2741,7 @@ xchar x, y;
 		    return;
 		}
 	}
-move_on:
+
 	if((!saleitem && !(container && cltmp > 0L))
 	   || eshkp->billct == BILLSZ
 	   || obj->oclass == BALL_CLASS