Minor VDC mode fixes and prep for ROM patcher

This is a combination bugfix and preparatory release.

1. A bug affecting operation of the VDC mode 5/6 on real hardware was fixed.
2. Changes were made to support the coming option to patch kernal ROMs so they directly support the idun-cart.

If you install using pacman, then you should also update idun-base. idun-vice is also updated for this release.