MSC: void _dos_setdrive( unsigned drive, unsigned *count )

	- prototype in dos.h

	- drive = drive to set as default;  1 = A:, 2 = B:, ...
	- count = receives simple count of total drives in system
	- does not return error if invalid drive is requested, use
	  _dos_getdrive() to see if requested drive was set

	- Turbo C uses setdisk()
	- see	INT 21,E   _dos_getdrive()