code: function mxCircleLayout(graph, radius)
  {
  	mxGraphLayout.call(this, graph);
  	this.radius = (radius != null) ? radius : 100;
  }
docs: Copyright (c) 2006-2015, JGraph Ltd
  Copyright (c) 2006-2015, Gaudenz Alder
   
  Class: mxCircleLayout
  
  Extends <mxGraphLayout> to implement a circluar layout for a given radius.
  The vertices do not need to be connected for this layout to work and all
  connections between vertices are not taken into account.
  
  Example:
  
  (code)
  var layout = new mxCircleLayout(graph);
  layout.execute(graph.getDefaultParent());
  (end)
  
  Constructor: mxCircleLayout
  
  Constructs a new circular layout for the specified radius.
  
  Arguments:
  
  graph - <mxGraph> that contains the cells.
  radius - Optional radius as an int. Default is 100.