INT 21,39 - Create Subdirectory (mkdir)

	AH = 39h
	DS:DX = pointer to ASCIIZ path name


	on return:
	CF = 0 if successful
	   = 1 if error
	AX = error code  (see DOS ERROR CODES)


	- creates specified subdirectory
	- returns error if directory already exists, element of the path
	  is not found, directory full or write protected disk