Reviewed the interaction of the AUTO mode, now we use the time attribute of the event...

Reviewed the interaction of the AUTO mode, now we use the time attribute of the events and calculate the velocity in the motion, doing a gimp like calculation. The velocity is calculated in each motion event using the last velocity and the current one, the SMOOTH_FACTOR controls the percentage of the new velocity we use.

* src/hildon-pannable-area.c: Replaced the time based algorithm
	for the AUTO mode.
	(hildon_pannable_area_motion_notify_cb): now we do not launch the
	timeout for the AUTO mode when we are still moving the cursor. We
	added also the velocity calculation in this function.
	(hildon_pannable_area_button_release_cb): launch the timeout in
	case we are in AUTO mode. There are still some constants here that
	come from the old implementation that should be reviewed and
	handled properly.