Issue #551 is causing problems

While it is true that ejecting a disc does not take a drive offline this new behaviour is causing problems.

All ejected drives now reply to a drive status command which makes FujiNet occupy up to all drives on the serial bus.

So we can no longer for example copy a real disk using a real drive to an ATR on the FujiNet because we have more than one drive with the same drive ID active on the bus.

Beyond this all software that relies on the old behaviour (drives going offline) will eventually have to be rewritten.

I guess it would be more compatible if the $E9 command (unmount drive image) would work like before and only if maybe AUX2 MSB is set the drive does not go offline. So we have both: compatibility with exisiting software and the means to unmount an image without having the drive go offline. Plus of course we can again use other drives to copy data from.

XeAtari

Start by tracing handling of the $E9 unmount-drive-image command and the drive status response behavior, including the proposed AUX2 MSB distinction. Reproduce the case with an ejected drive and a real drive on the serial bus; done means existing software compatibility is restored while the alternate unmount behavior remains available.

Written by the indexing model from the issue text.