The DSK1 emulation fix I applied seems to have worked.  2 bytes of code was
what it took.(and a LOT of head-scratching).

1. MDOS-  All DSK devices/operations now work following a SCSI operation.
I'll do some more thorough testing, but the test scenarios which fail in
MDOS650 work in my revised code.  dskx emulation only applies to emulate
files remapped as a DSK device. MDOS 221 and 650 operate in similar manner.
COPY CON to DSK device works following SCSI operation.  TYPE DSKx.filename
now works following a SCSI operation.

2. GPL
DSK1 emulation works.  I can "OLD DSK1.file" and it will load from HFDC dsk1
subdirectory.  If not present there, it will fail over to regular floppy.

I can "OLD DSK.vol.file" and it will search HDS1.DSK. first, then each of
the 4 floppy drives.  It will load from the HDS1. folder... and from a drive
mapped to DSK1... but if it searches the drives and finds the volume on an
HFDC floppy NOT at DSK1, it fails.  This is consistent in MDOS 221 and 650 -
probably a bug not noticed before.  I have added it to my list; and I think
I know where the bug is and will review tomorrow.

Emulate files work when remapped.  If the emulate is remapped to DSK1, it
will search out the HFDC.DSK1 folder before the emulate itself.  This sounds
like the right order of operation.  If not, 221 and 650 are both wrong.