Pistons and sticky pistons
--------------------------
* These blocks are only available if digilines and/or mesecons are loaded.

Pistons push up to the setting Maximum piston nodes (default 15) in front
of the pusher when extended. Sticky piston draw back a single node in
front of the pusher when retracted. Piston also act as a digilines
conductor.

Sticky blocks are also supported. Any sticky block structure attached to
the pusher will also be pushed, up to the maximum setting. Any free blocks
(not attached to the sticky blocks) in front will be pushed up to the
maximum setting. This limit is from the pusher, not the sticky block. When
retracting a maximum of one free block depth will be pulled. Any sticky
block structure extending laterally by more than half the maximum limit
will not be pushed.

Any entities in front of or standing on a moving node are pushed/pulled,
if nothing is in the way of their base position. Any entities against a
sticky face are not pulled.

UI

Channel - digilines channel of piston.
Single move - pusher extends 1 node if checked, otherwise 2 nodes.

Mesecons
	Piston extends while power is turned on.

Digilines messages

"extend n"
	Extends the piston pusher to extent n (0, 1 or 2). If n is not given
	pusher extends to maximum extent. 0 is retracted.

"retract"
	Same as 'extend 0'.

"single"
	Sets piston to single move mode.

"double"
	Sets piston to double move mode.
