CNodeDefManager::get()
VoxelManipulator::addArea()

Set content to fallback on AddNode failure
Consider node list requests with no results as failed

Check if mesh is here before adding to meshcollector.

Fix deleting the meshes.

This also cleans up settings a bit

Protocol version bump.

Pass drawtype and material type to shaders.
Move shaders generation to startup only.
Allow assign shaders per tile.
Initial code to support water surface shader.

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.