Fix mention_walls distinguishing unseen walls from solid stone

Bumping into an unseen wall reported "a wall" instead of "solid stone",
even though you could not know it was a wall when looking at it.

Use the same method when looking at glyphs on the map instead of
the map location type.

Fixes #318

doc/fixes3-7-0.txt

@@ -765,6 +765,7 @@ falling down a hole or trapdoor will cause damage proportional to fall height
 stinking gas clouds block line-of-sight
 covetous monsters will teleport to downstairs or upstairs to heal
 have fake player monsters use verbalize instead of pline when reacting to chat
+fix mention_walls distinguishing unseen walls from solid stone
 
 
 Fixes to 3.7.0-x Problems that Were Exposed Via git Repository