U162 - killing shopkeeper with unpaid thrown objects

U162 - killing shopkeeper with unpaid thrown objects
While an object is being thrown, it isn't on any list.  This means that
killing a shopkeeper with an unpaid object wouldn't be able to clear the
unpaid bit.  By the time the object lands, the shopkeeper is gone, and then
it's too late.  Added a new global to track a thrown object, set it and later
clear it in throwit(), also clear it as needed in dealloc_obj(), and check
it in setpaid().  It should be possible to use this global to avoid losing
thrown objects during hangup saves as well.  But that can wait.