Bug was introduced in 16a7c9fe, caused by
the fact that sometimes nodes are dug by nil,
i.e. the way the chisel is dug up automatically
in the chiseling process.
- Make handhold nodes glow, to visually simulate the player
character's now "familarity" with them by feel. We have to
represent it synesthetically because the game only gives us
sight and sound to work with.
- Make floors "scalable" so that they glow, even though they
don't affect maneuverability.
The effect of this is to allow a player who has fallen into a dark
cavern to navigate, slowly, by feel, allowing more extensive
self-rescue possibilities.
