When underwater, map adjacent lava as lava rather than as "not water".
The Valkyrie quest has lava adjacent to water and the hero ought to
be able recognize it while immersed so she doesn't try to climb out
of water directly into lava.
When the color option is disabled and lava uses the same symbol as
pool or as water (which is the case for default ascii, DECgraphics,
and IBMgraphics), apply the detected-monster display effect to lava.
For tty, this will draw it in inverse video if the use_inverse
option is enabled. (Assumes non-tty will nearly always be using
color so not care.) Creating a separate mapglyph special attribute
for B&W lava instead of overloading MG_DETECT ought to be done but
I didn't want to modify any interface code.
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