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/detect.c

@@ -890,6 +890,7 @@ struct obj *obj;
     }
     You("peer into %s...", the(xname(obj)));
     nomul(-rnd(10));
+    multi_reason = "gazing into a crystal ball";
     nomovemsg = "";
     if (obj->spe <= 0)
 	pline_The("vision is unclear.");