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.

tubes.lua

@@ -577,31 +577,10 @@ if enable_mese_sand_tube then
 	})
 end
 
-local function facedir_to_dir(facedir)
-	--a table of possible dirs
-	return ({{x=0, y=0, z=1},
-					{x=1, y=0, z=0},
-					{x=0, y=0, z=-1},
-					{x=-1, y=0, z=0},
-					{x=0, y=-1, z=0},
-					{x=0, y=1, z=0}})
-					
-					--indexed into by a table of correlating facedirs
-					[({[0]=1, 2, 3, 4, 
-						5, 2, 6, 4,
-						6, 2, 5, 4,
-						1, 5, 3, 6,
-						1, 6, 3, 5,
-						1, 4, 3, 2})
-						
-						--indexed into by the facedir in question
-						[facedir]]
-end
-
 local function facedir_to_right_dir(facedir)
 	
 	--find the other directions
-	local backdir = facedir_to_dir(facedir)
+	local backdir = minetest.facedir_to_dir(facedir)
 	local topdir = ({[0]={x=0, y=1, z=0},
 									{x=0, y=0, z=1},
 									{x=0, y=0, z=-1},