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"

src/priest.c

@@ -475,6 +475,7 @@ int roomno;
 	    if (flags.verbose)
 		You("are frightened to death, and unable to move.");
 	    nomul(-3);
+	    multi_reason = "being terrified of a demon";
 	    nomovemsg = "You regain your composure.";
 	}
     }