Rewrite _set_nearest_monster_foe.

With the previous one_chance_ins, it was failing quite often with enemies in view.

Created by  Robert Vollmert  on October 29, 2009
USNTAFJF3IA4JD6E26RY4MHVMFBEKRBHFJC6KV3MAF2MFW4G4MDAC
Change contents