Reveal the map boundary

[Hellmonk]

One potential issue with this change is that the passwall targeter can
reveal map bounds, because the ray won't render. I'm not sure there's
anything to be done about this, though, and this is far from the only
thing that does (e.g. setting exclusions on out of bounds positions).

Sometimes I want to dig a wall and waste a turn because it's the edge of the map. Now that I know about these cool exploits, I can tediously avoid this. Reveal the map's outer edge imo, the existing behavior is silly anyway.

[advil]

If the exclusion thing (which I'm not sure is widely known? I only discovered it while testing the passwall changes) can't be easily fixed, then yeah, I'm not sure what other solution there might be to this, short of some major rewrite of how level bounds work.

Btw I may add a dig targeter using the same rendering technique as passwall, which would also solve your immediate complaint. Just haven't gotten to it yet.

[aidanholm]

I've been planning to make the map boundary use unbreakable rock walls, but haven't gotten around to it yet. |amethyst mentioned something on IRC (2018-03-15) about wanting them to appear like regular walls until they're in LOS.