The C BIOS has been modified since publication of the System Guide.
A new #define is required in the BIOSTYPE.H file when a loader BIOS
is being generated.  The #define is for a symbol called "BOOTDSK".
This should be set to the number of the disk from which the loader
bios is to read the CPM.SYS file, 0->A, 1->B, ... .
LOADBIOS.H and BIOS.C have been changed to reflect this new usage.