Disc image updates

When the disc image is updated I would find it extremely helpful if there was an incremental update as well so that those with the last even-numbered release (say 5.16 on the Iyonix or 5.18 on the Iyonix) or the last supported version where there has been no even-numbered release (Beagleboard XM or Pandaboard ES both via RComp or Raspberry Pi RC8 via ROOL) had a changed-components-only version of HardDisc4 [including !Boot.Choices] to copy over the top of their existing HardDisc4.

The IwoUpWych application did just that.