Keep epsilon when manually modified by the player

[Mikolaj]

Currently, whenever flinging at an actor, projectile path (determined by epsilon, at seps field), get changed at the last moment to avoid any actors and and obstructions in the way. The workaround to hit many actors with a piercing missile is to change targeting mode from at-enemy to at-position.

Instead, epsilon should be auto-tuned only whenever a new actor is targeted or when player's turn starts and actors or obstacles are noticed to have appeared in the way (debatable). It should never be changed otherwise. This results in WYSIWYG.