SYNOPSIS
	int set_heart_beat(int flag)

DESCRIPTION
	Enable or disable heart beat. The driver will apply
	the lfun heart_beat() to the current object every 2 seconds,
	if it is enabled. If the heart beat is not needed for the
	moment, then do disable it. This will reduce system overhead.
	
	Return true for success, and false for failure. Specifically,
	it will fail if the heart beat function has been disabled,
	which it will be if there is a run time error in it.

SEE ALSO
	heart_beat(A), call_out(E)