Fix T41818: Missing refresh on Undo for nodes (mask example)

Added a special notifier now NC_WM|ND_UNDO in order to deal with such cases
and now compositor/image will refresh when undo happens.

There are much more ways to fail compo to update the resul, like undoing
while it's not visible and so, but as mont29 said -- let's at least fix
obvious crap in the workflow.

source/blender/editors/space_image/space_image.c

@@ -539,6 +539,12 @@ static void image_listener(bScreen *sc, ScrArea *sa, wmNotifier *wmn)
 			}
 			break;
 		}
+		case NC_WM:
+			if(wmn->data == ND_UNDO) {
+				ED_area_tag_redraw(sa);
+				ED_area_tag_refresh(sa);
+			}
+			break;
 	}
 }
 

source/blender/editors/space_node/space_node.c

@@ -420,6 +420,9 @@ static void node_area_listener(bScreen *sc, ScrArea *sa, wmNotifier *wmn)
 						}
 					}
 					break;
+				case ND_LAYER_CONTENT:
+					ED_area_tag_refresh(sa);
+					break;
 			}
 			break;
 
@@ -507,6 +510,11 @@ static void node_area_listener(bScreen *sc, ScrArea *sa, wmNotifier *wmn)
 				ED_area_tag_refresh(sa);
 			}
 			break;
+		case NC_WM:
+			if(wmn->data == ND_UNDO) {
+				ED_area_tag_refresh(sa);
+			}
+			break;
 	}
 }
 

source/blender/editors/util/undo.c

@@ -213,6 +213,7 @@ static int ed_undo_step(bContext *C, int step, const char *undoname)
 	}
 	
 	WM_event_add_notifier(C, NC_WINDOW, NULL);
+	WM_event_add_notifier(C, NC_WM | ND_UNDO, NULL);
 
 	if (win) {
 		win->addmousemove = true;

source/blender/windowmanager/WM_types.h

@@ -249,6 +249,7 @@ typedef struct wmNotifier {
 #define ND_DATACHANGED		(3<<16)
 #define ND_HISTORY			(4<<16)
 #define ND_JOB				(5<<16)
+#define ND_UNDO				(6<<16)
 
 	/* NC_SCREEN screen */
 #define ND_SCREENBROWSE		(1<<16)