This avoids warnings shown by Minetest and improves the nodes' look when a bilinear filter is enabled.
Since the textures are also used as inventory images, I didn't remove the transparency from the texture files.
* Luablock: Fix the missing position argument when executing the lua code fails
* Wireless: Fix the missing id argument
* Localize several variables
* Some other small changes, e.g. dead code removal
