ElementHandler.addOpposite(): fixed bug
ElementHandler.addOpposite(): fixed bug

Now correctly finds out whether an equal opposite is already registered.

ariyapour/xml3d.js,ariyapour/xml3d.js,Fiware/webui.Xml3d.js,CCLDESTY/xml3d.js,Fiware/webui.Xml3d.js,xml3d/xml3d.js,CCLDESTY/xml3d.js,xml3d/xml3d.js