Change pit behavior to always mark a non-flying poly'd player as trapped in
a pit, even when Passes_walls is set. This allows players polymorphed into
xorns to descend into pits and pick things up. In this case, any attempt
to move out of the pit now takes a turn but always succeeds. Also fixed
a related bug (w/o ID) that a player could become trapped as if in a pit
when leaving xorn form because u.utrap wasn't checked, and simplified the
code since the extra Passes_walls checks are no longer needed. Also
updated code in sit.c that duplicated uteetering_at_seen_pit.
b661f86e67