stop leaking clone_node() function outside of pipeworks namespace
fix bad lighting on one-way tube
Split pipe and tube autorouting functions into separate files.
get rid of some extraneous print statements
Make the tube_connects={} method work properly for technic devices.

Also phase out "old new" API, leaving only the "tube_connects={}" method,
as nothing in technic or pipeworks uses it.

Fix a few more places where minetest.facedir_to_dir() was duplicated, since
that code is part of Minetest 0.4.8.
limit tube autoconnect checking to only run if tube.connect_sides
is defined for a particular node (rather than the whole tube table).

Also, tweak wording of an error message to account for line
numbering changes.