#178 Trigger auto-pickup only if the player moves

[Andreas Kirschbaum]

Consider the following:
- player enables 'pickup 4 (pickup all items)
- player drops some items to the ground
- player tries to move away but is blocked for any reason
- now the server auto-picks up all items

This is probably not what the player intended. Instead, auto-pickup should only trigger if the player's location changes.

Note: this normally happens while fighting monsters: the player drops some items to reduce weight, then tries to walk away. If by now a monster has walked in front of him, he again picks up the items he tried to get rid of.