fix #H7065 - clairvoyance shows trap over monsters

and over the hero.  3.6.0's clairvoyance tried to show things in
a non-standard sequence, which was intentional but had unintended
side-effects like the disappearing monsters complained about in the
report.  To make it work as intended would have required --More--
whenever it kicked in, which is much too intrusive when it happens
every N turns rather than when explicitly casting the spell.

Redo it substantially, and give preference to monsters over objects,
objects over traps, and traps over underlying terrain like normal
vision-based display does.  It now detects all monsters within its
bounding box but shows ones which aren't directly in view as
"unseen monster" unless via spell cast at skilled or expert, or at
basic when also having intrinsic clairvoyance.

doc/fixes36.2

@@ -194,6 +194,8 @@ avoid potential buffer overflow if object with very long name knocks other
 	objects down stairs when dropped, thrown, or kicked there
 #wizintrinsic for 'flying' didn't update status line when flying ended
 #wizintrinsic for 'warn_of_mon' didn't set any type of monster (now grid bugs)
+clairvoyance would show trap instead of a monster on/in that trap, which was
+	intentional, but when clairvoyance finished the monster wasn't shown
 
 
 Fixes to Post-3.6.1 Problems that Were Exposed Via git Repository