INT 1A,6 - Set Real Time Clock Alarm (XT 286,AT,PS/2)

	AH = 06
	CH = hours in BCD
	CL = minutes in BCD
	DH = seconds in BCD

	on return:
	CF = 1 if alarm already set or clock inoperable

	- alarm setting is not relative like some sources claim, but the
	  actually clock time the interrupt should occur
	- settings values must be in BCD
	- when the alarm time is reached INT 4A is executed
	- INT 4A vector should be replaced with address of the alarm
	  handling interrupt routine before setting the alarm
	- INT 1A,7 should be called to disable the RTC alarm