ENH: Push outgoing messages when the connector node becomes active and OpenIGTLinkIF.pushOnConnect attribute is 1. See Slicer Bug Tracker #3501.
ENH: Update vtkMRMLIGTLConnectorNode::PushNode() to prevent other connector nodes from sending the pushed node.
ENH: Add 'Push on Connect' checkbox in I/O configuration. Rename 'pushOnConnection' attribute to 'pushOnConnect' (value must be either 'true' or 'false')
ENH: Hide 'Push on Connect' check buttons for incoming nodes.
ENH: Fix vtkMRMLIGTLConnectorNode.cxx to merge 3501-send-all-outputs-on-connection branch.