Hero remembers trapped boxes

After finding a trap on a chest or a large box, remember it
as trapped: "You see here a trapped large box."
Randomly generated chests and boxes can be obviously trapped.
Allow defining obviously trapped containers via lua.

Invalidates saves and bones.

include/sp_lev.h

@@ -156,7 +156,7 @@ typedef struct {
     int quan;
     short buried;
     short lit;
-    short eroded, locked, trapped, recharged, invis, greased, broken,
+    short eroded, locked, trapped, tknown, recharged, invis, greased, broken,
           achievement;
 } object;