The default symbol for lit and unlit corridors are the same. This makes
the lit_corridor option a no-op where the defaults are used and also means
that using a light scroll/spell a corridor has no obvious effect. To
address that, I special-cased the lit corridor symbol and change its color
to bright white when its the same symbol as the unlit corridor symbol (I
didn't change the default color since I thought that made the lit corridor
look strange using the windows console interface).
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