INT 21,67 - Set Handle Count (DOS 3.3+)

	AH = 67h
	BX = new maximum open handles allowed

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

	- gives program control of the number of files simultaneously open
	- if CX is less than the current number of open files the change
	  will take effect when the number of open handles falls below
	  the new limit
	- this function allows the application to use more than 20 files,
	  up to the FILES=N limit
	- earlier copies of IBM DOS 3.3 sometimes incorrectly allocates
	  memory (up to 64K) if an even number of handles is requested
	- only the first 20 files handles are copied to a child process
	  regardless of the max number of files
	- it is possible to allocate more than 255 file handles but it is
	  difficult to use more than 255