made the RIGID flag work for containers

Container without that flag add the volume of their content to the total volume of the item.
Container with that flag show just the containers volume and ignore the content.
fix waterskin2, should have different volume, not bash modi
-fixed bug where dynamic zombie groups were being flagged as hordes, causing them to wander and be visible on the overmap
Merge remote-tracking branch 'dda/pr/6258' into dda-master

* dda/pr/6258:
  fix waterskin2, should have different volume, not bash modi
  made the RIGID flag work for containers

Conflicts:
	src/item.h
Merge remote-tracking branch 'dda/pr/7414' into dda-master

* dda/pr/7414:
  -fixed bug where dynamic zombie groups were being flagged as hordes, causing them to wander and be visible on the overmap
Don't autopickup ammo, fixes #7384.