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.

	Disabling an already disabled heart beat (and vice versa
	enabling and enabled heart beat) counts as failure.

SEE ALSO
	heart_beat(A), call_out(E)
