Index-Input instead of Index-enable signal

If Implemented in hal, the basic idea would be to
set spindle-sync true, do a slow velocity spindle rotate
until spindle-sync becomes false and then run the orient
cycle.

 It would be nicer if this was implemented in the orient
component, and better still LinuxCNC, but a hal
implementation should work identically.
 

A kludgy way to do this in the Gcode is with a very tiny G33.1 move at low spindle speed. That will reset the encoder to the index.