Leaflet FeatureGroup extends LayerGroup

From "http://leafletjs.com/reference.html#featuregroup"
L.FeatureGroup

Extended LayerGroup that also has mouse events (propagated from members
of the group) and a shared bindPopup method. Implements ILayer
interface.
Merge pull request #1055 from flxf/LFeatureGroup

Leaflet FeatureGroup extends LayerGroup