Lua: Traps without victims

Traps may get corpses generated on them on early dungeon levels,
to warn off fragile starting heroes. Allow creating traps in lua
without the corpse.

include/hack.h

@@ -584,6 +584,7 @@ enum bodypart_types {
 #define MKTRAP_MAZEFLAG      0x1 /* trap placed on coords as if in maze */
 #define MKTRAP_NOSPIDERONWEB 0x2 /* web will not generate a spider */
 #define MKTRAP_SEEN          0x4 /* trap is seen */
+#define MKTRAP_NOVICTIM      0x8 /* no victim corpse or items on it */
 
 #define MON_POLE_DIST 5 /* How far monsters can use pole-weapons */
 #define PET_MISSILE_RANGE2 36 /* Square of distance within which pets shoot */