layers when passed an array of layers instead of a single layer with
the constructor. This changeset also introduces a new layer type,
Layer.Vector.RootContainer, which will be set as the topmost layer by
the SelectFeature control and collect the svg/vml/canvas roots of
multiple vector layers. r=crschmidt (closes#1666)
git-svn-id: http://svn.openlayers.org/trunk/openlayers@9116 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf
