BUGFIX: GLADEVCP of configs/araisrobo/miller

Prevent issue MDI command to stop spindle when it's already stopped
BUGFIX to RIGID_TAP() at emccanon.cc

* let RIGID_TAP() honor the MAX_VEL for cartesian_move, and
  constrain the spindle velocity if it is required.
* Restore oritinal getStraightVelocity() from joints_axes3 branch
* add feed_per_spindle_revolution to canon data structure
Merge branch 'feature/usb-rigid-tap' of github.com:araisrobo/linuxcnc into feature/usb-rigid-tap