breaking lock of shop chest (trunk only)

From the newsgroup:  you weren't charged anything if you broke the
lock of a box or chest which was owned by a shop.  Force the hero to pay
for the damaged container; any contents remain owned by the shop and don't
affect the cost of the forced purchase.  This existing entry in fixes35.0
is adequate to cover the fix:

various actions--such as enchanting--performed on an unpaid shop object
	either force the hero to buy the item (when its value is lowered) or
	increase the current bill (when its value is raised)

include/extern.h

@@ -958,6 +958,7 @@ E int NDECL(picklock);
 #endif
 E boolean FDECL(picking_lock, (int *,int *));
 E boolean FDECL(picking_at, (int,int));
+E void FDECL(breakchestlock, (struct obj *,BOOLEAN_P));
 E void NDECL(reset_pick);
 E int FDECL(pick_lock, (struct obj *));
 E int NDECL(doforce);