Some location update messages do not contain the 't' (trigger) key. Before the change in 0.94 to
entity based trackers, these would default to source_type of 'gps' (due to default parameter
value in async_see method.) To mirror this behavior in the new entity based tracker, the
source_type property should default to SOURCE_TYPE_GPS under the same conditions.
Paulus Schoutsen
Phil Bruckner
Martin Hjelmare