Dropped items no longer dissappear.

The directional drop code was substantively different from the regular drop code; directional drops do not duplicate items when dropping into full vehicle trunks, even on builds pre-#1401. Since the directional drop code actually works, I copy-pasted the relevant parts over the regular drop code, changed dirx/diry to u.posx/u.posy, and the result doesn't duplicate items and actually drops dropped items.

Hopefully I haven't horribly broken anything this time.