Handle moving conductors

[numberZero]

From #404:

Place a mesecon at the crosshair, and it will crash. WARNING: it breaks the world! Removing mesecon_actionqueue is mandatory after such experiment, and there may be consequences. The reason is that it can’t handle moving conductors well at all. It queues activation of the left movestone, but on the next step, the right movestone moves first, substituting it with the gate. The gate expects a named rule, but gets unnamed one that was queued for the movestone.

[numberZero]

See also #405, #502.