maintenance related: this cleans up a global flag (_OPENLAYERS_SFL_), replacing it with something in the OpenLayers namespace, and adds documentation/comments to the code here that weren't before. Approved by El Chairman Uz. git-svn-id: http://svn.openlayers.org/trunk/openlayers@3543 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf