TC: int bdosptr( int dosfun, void *argument, unsigned dosal )

	- prototype in dos.h

	- make DOS system call for function dosfun, passing POINTER
	  to values via argument and passing AL via dosal
	- use for small or large memory models
	- returns value of AX set by system call, else -1 on failure
	  (where errno & _doserrno are then set)