Allows the sliding of pipework along floors

Allows pipes to be slid along the floor, not only does this make laying
pipes easier, but you can now lay pipes under machinery without having
to remove them.
Longer time taken to drill a pipe through a r_wall

Added a message too to the driller that it's going to take a while.
Merge pull request #353 from Bone-White/master

Slide pipes along floors