This way flowing liquids actually show the backface when specified to
do so. Without this, TileDefs where by default initialized with
backface_culling = true and never set otherwise.

For backwards compatibility, an old client connected to a new server,
or a new client connected to an old server will behave like before
i.e., backface_culling is always true.

This way, plants actually show the real backface on their back side,
i.e., the front face mirrored around the vertical axis, instead of
showing the front face on both sides. This looked weird when the
texture was not symmetrical around the vertical axis.

Fix more things I forgot for attached players. Such players will now properly see themselves moving when attached, and the server will read their position accordingly

Fix attached players being able to bob their view and generate foostep sounds by pressing a movement key (running in place)

Fix some remaining issues with attachments, now they work. Tested with object->player and player->player attachments

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 :) .

Add after_destruct and cache the existence of on_construct, on_destruct and after_destruct for quick skipping when a node does not have them

Switch the license to be LGPLv2/later, with small parts still remaining as GPLv2/later, by agreement of major contributors