block_movement behaves funny with aots

the function move.c:bewegung_blockiert_von behaves funny in two ways:
- if there is more than one unit with highest perception, only the last one is checked for an amulet of true seeing
- if this unit has more than one amulet, each amulet gives a 10% bonus on the chance to stop foreign units' movement; if the unit has 7 amulets, the chance is 100%. I doubt that this was intended.
The merge request fixes both issues, adds testing and makes probabilities configurable.