INT 1A,4 - Read Real Time Clock Date (XT 286,AT,PS/2)

	AH = 04


	on return:
	CH = century in BCD (decimal 19 or 20)
	CL = year in BCD
	DH = month in BCD
	DL = day in BCD
	CF = 0 if successful
	   = 1 if error or clock not operating

	- calling this interrupt will update the DOS maintained date and
	  reset the BIOS Data Area date rollover flag at 40:70
	- see	RTC