It's possible to turn a motor on forward and backward at the same time

[hbradio]

This is not great for the motor.

If a motor is running then turned on in a different direction without first being stopped, rovercode should automatically shut off the first direction pwm pin.

I'm not sure at what level this should happen. It seems safest to do it on the rover side instead of the client side. But, it'll need to get info from the client at connection to know what pins are forward/backward pairs.