NO_CORPSE_ROTTING corpse will dissapear after a while

A fix for #69. NO_CORPSE_ROTTING should just mean the corps of a unit with this property cannot turn into a vampire, and it would not get dragged to a graveyard.

Before this fix, setting this property on a unit would mean its corpse would never dissapear from the map.

src/thing_corpses.c

@@ -204,9 +204,9 @@ TngUpdateRet update_dead_creature(struct Thing *thing)
                 set_thing_draw(thing, i, 64, -1, 1, 0, 2);
             }
         } else
-        if ( corpse_is_rottable(thing) )
+        if (thing->byte_14 != 0)
         {
-            if (thing->byte_14 != 0)
+            if ( corpse_is_rottable(thing) )
             {
                 if (thing->health > 0)
                     thing->health--;
@@ -222,6 +222,12 @@ TngUpdateRet update_dead_creature(struct Thing *thing)
                     return TUFRet_Deleted;
                 }
             }
+        } else
+        {
+            if (game.play_gameturn - thing->creation_turn > game.body_remains_for) {
+                delete_thing_structure(thing, 0);
+                return TUFRet_Deleted;
+            }
         }
     }
     if (subtile_has_water_on_top(thing->mappos.x.stl.num, thing->mappos.y.stl.num)) {