node) brings up a context menu that allows you to 1) Cancel the
current drag operation for that robot, 2) bring up the Emulab shownode
page in another window, and 3) set the orientation for the robot using
a popup dialog input box. This allowed me to clean up some of the
table handling code, and fix a glitch whereby a value left inside a
cell being edited caused the a cancel drag operation to immediately
start a new one.