+ // Queue exits (i.e. successors of rets/endpads) with the parent color.
+ // Skip any exits that are catchendpads, since the parent color must then
+ // represent one of the catches chained to that catchendpad, but the
+ // catchendpad should get the color of the common parent of all its
+ // chained catches (i.e. the grandparent color of the current pad).
+ // We don't need to worry abou catchendpads going unvisited, since the
+ // catches chained to them must have unwind edges to them by which we will
+ // visit them.