Add more explicit helpless reasons

Instead of just "while helpless", the death reason will tell
more explicitly why the player was helpless.  For example:
"while frozen by a monster's gaze"

doc/fixes35.0

@@ -1107,6 +1107,7 @@ cursor positioning ignores uninteresting dungeon features
 allow reading many more items
 when you're hiding under something a zap downward should not hit that
 	something, while a zap upward should
+show more explicit reason why player was helpless at death
 
 
 Platform- and/or Interface-Specific New Features