more weight tweaks

Update some potential weight issues.  Eggs won't hatch when in
containers so they weren't affected but add some bulletproofing.
Corpse revival from inside containers was already ok too, so
effectively there's no change except for making container_weight() be
global instead of local to mkobj.c.

src/zap.c

@@ -1069,6 +1069,7 @@ revive(struct obj *corpse, boolean by_hero)
         m_useup(corpse->ocarry, corpse);
         break;
     case OBJ_CONTAINED:
+        /* obj_extract_self() will update corpse->ocontainer->owt */
         obj_extract_self(corpse);
         obfree(corpse, (struct obj *) 0);
         break;