don't leave follow mode on mapmove for a variable zoom
the user may want to use different zooms in follow mode (for example
if he rides a bike or drives a car)...unfortunately, leaflet triggers
maps movestart event _before_ the zoomstart event. this makes it
impossible to differentiate between a mapmove triggered by a zoom-event
or a move-event. the user can leave the follow mode by pressing the
getLocation button...this should be enough.