lookat issues for unknown/solid rock/dark room

lookat issues for unknown/solid rock/dark room

Fix two things with the ';' and '/' commands, both for looking at blank
space.  The list of possibilies included "a dark part of a room or the
dark part of a room" even though the code involved goes out of its way
to avoid redundant clauses.  S_stone let dark part be prefixed by 'a',
S_room and S_darkroom forced it to be 'the' which is better phrasing
but outsmarted the redundancy check.  Make S_stone's use of "dark part
of a room" force 'the' too.

That's trivial; this is more complicated:  the new maze variations
exposed/aggravated an issue that's been there all along.  In a non-
WALLIFIED maze, doing look-at on the solid stone in-place-of-wall
next to you reported "dark part of a room" which is clearly wrong when
you can tell it's not a room.  (The same thing happens in any ordinary
corridor, but players rarely try to identify blank space next to them
it that circumstance so it hasn't mattered very much.)  This change
results in look-at listing "unexplored" and "stone" as additional
possibilities when looking at blank spots.  Final description will be
"unexplored" instead of dark room if you haven't seen the spot, "stone"
if you have and that's what it is, or "dark part of a room" otherwise.