Make coordinates stored for drop/pickup/move activities relative to the player.

This will break pickup/drop/move operations that were interrupted by an auto-save, but I can't bring myself to care about such an obscure corner case.  They will just fail with some weird messages and can be started over.
Uh, (e) pickup doesn't happen in vehicles unless it's your own tile.  Check this when on foot?  I had it get to the list, accept my picks, and then not make the grab.