Add Dual Stepper Homing For Single Axis

[graybilldustin]

For machines that use 2 steppers to drive a single axis with one channel set as a slave channel, it would be nice to allow both steppers to home at the same time. Typically a machine that is set up like this, like a Gantry style router or plasma table, does not have the 2 steppers physically linked. When the controller is powered off the steppers can go out of sync with each other causing a skew in the axis when power is reapplied.

[leadgtr7]

Duplicate of Issue #218

[klack770]

With the latest update, this is my only remaining request. Is this on the radar?