Add drill table layer; regenerate Gerbers in vendor-approved format.

The drill table was made with drillegend-stack.ulp.  It has a problem deleting
an existing drill table (see
   http://www.eaglecentral.ca/forums/index.php/mv/msg/46577/145423/
) so I've saved the .brd file with the drill legend as XOrduino2-drilltable.brd.
If changes are necessary to XOrduino2.brd, regenerate XOrduino2-drilltable.brd
from XOrduino2.brd after making the changes.
Hall Effect Sensor Test Shield, v1.
Chack in updated BOM for XOrduino2 v8 boards.