Changes for 2.3.9

• Improved LayeredDigraphLayout routing of Bezier links at NoSpot nodes
• The DiagramEvent.subject collection for an "ExternalObjectsDropped" event now includes the whole collection, even if the number of dropped Parts is greater than Diagram.maxSelectionCount
• Fixed SVG rendering of some Panel clipping regions.
• Fixed SVG opacity on Panels.
• Fixed animation when tree-collapsing nodes with multiple tree parents.