fix more your corpse cases

- new cxname() to simplify doing the right thing in increasingly common cases
- use for bullwhip snagging
- in shopkeeper offer code
- in a couple other existing places rather than duplicating CORPSE checks
- use singular(...) in "swings" cases, since only one can hit.  Singular uses
  corpse_xname automatically when appropriate

src/apply.c

@@ -2163,7 +2163,7 @@ struct obj *obj;
 	    const char *mon_hand;
 	    boolean gotit = proficient && (!Fumbling || !rn2(10));
 
-	    Strcpy(onambuf, xname(otmp));
+	    Strcpy(onambuf, cxname(otmp));
 	    if (gotit) {
 		mon_hand = mbodypart(mtmp, HAND);
 		if (bimanual(otmp)) mon_hand = makeplural(mon_hand);