fix #U1202 - shop robbery oversights

fix #U1202 - shop robbery oversights

     A user reported that when breaking potions inside a box in a shop, he
wasn't charged for them.  The code was calling stolen_value() as intended,
but that routine only charged for types of items which the shop normally
carries.  That meant that breaking the contents of a box in a general
store would charge for them but doing so in a tool shop would, not even
though the tool shopkeeper would gladly sell such things when you picked
them up instead of causing them to go away.

     When fixing this, I noticed that stolen_value() was only charging
for single items.  Most of the time that was right, because throwing and
kicking things always split one off, but there are cases (such as zapping
a wand of teleportation at shop goods) where an entire stack gets stolen
as a group.  This makes stolen_value() handle all quantities.