Targeter for monster Fulminant Prism; some related bug fixes.

Monsters try to place prisms such that they cover the maximum number of
spaces the target could be at in 30 aut (the prism's detonation time).

Once again, ghosts will be our testing ground for this; one suggested
use for this is deep elf conjurers (who have too many bolt spells right
now).

This also fixes the bug of "hit from afar by [bennu | fulminant prism]"
(both have only occurred once at the time of this commit).