Version 0.4.3-rc0; increase PROTOCOL_VERSION due to backwards-incompatible InventoryList width field

Remove "Unknown inventory identifier" deserialization errors, because they can break forward compatibility

- Don't select blocks for drawing in every frame
- Sort meshbuffers by material before drawing

- You have 2 stacks: a with x items and b with y<x items
- Take a with your mouse and place it on b
- Whole stack a moves to b
- (y * 2 - x) items move from b to a
- (x - y) items are left to the mouse cursor

- Display message when associating a key already in use
- Fix issue for not beeing able to assign space to an action
- Cleaning up
- Make it build (by celeron55)

"aux1_descends" setting switches to the old descend control.

Opaque water's solidness was being set to 2, like a normal node.
When you swim, it is treated like a solid block, and the display
goes black.  Setting it to 1 like transparent water allows you to
see.

It looks somewhat awkward when you swim, look up, and see an opaque
wall of water (the surface), but there isn't much that can be done
about it.  If you made the water transparent so it looked good,
it would defeat the purpose :) .

The items will now just disappear when dropped.

Commands moved:
 /me
 /status
 /time
 /shutdown
 /ban
 /clearobjects

Those functions are:
 * minetest.get_ban_list()
 * minetest.get_ban_description(ip_or_name)
 * minetest.ban_player(name)
 * minetest.unban_player_or_ip(ip_or_name)

minetest.get_server_status()
minetest.request_shutdown()
EnvRef:clear_objects()

This allows the removal of nodes with unknown types.
get_item_callback() (C++) would fail if a node has an unknown type.  Now it
will try using the callback from minetest.nodedef_default in this case.
Also, minetest.node_dig() (Lua) was altered to always allow digging when
the node definition is empty (i.e. unknown node).