Small usability tweaks in Compositor:

- After making a Group, internal socket values are now copied to the
  group node, so an execute will give identical results
- After ungrouping, the cyclic dependency tagging didn't work well in
  all cases, showing a red noodle line and giving composite errors.
  For time being solved by calling the NodeSort twice.
- Viewer nodes now get previews updated always (used to be only the active)
  Note: this is not for previews inside of groups!

source/blender/src/editnode.c

@@ -531,7 +531,6 @@ void node_ungroup(SpaceNode *snode)
 	else {
 		if(nodeGroupUnGroup(snode->edittree, gnode)) {
 			
-			ntreeSolveOrder(snode->edittree);
 			BIF_undo_push("Deselect all nodes");
 			allqueue(REDRAWNODE, 0);
 		}