Tracker: Thumbnail attribute changes should cause an icon refresh.

This way, a full mimeset need not be run to trigger an icon update,
and also other applications can write thumbnails and trigger updates.

src/kits/tracker/Model.cpp

@@ -898,7 +898,8 @@ Model::AttrChanged(const char* attrName)
 	if (attrName != NULL
 		&& (strcmp(attrName, kAttrIcon) == 0
 			|| strcmp(attrName, kAttrMiniIcon) == 0
-			|| strcmp(attrName, kAttrLargeIcon) == 0)) {
+			|| strcmp(attrName, kAttrLargeIcon) == 0
+			|| strcmp(attrName, kAttrThumbnail) == 0)) {
 		return true;
 	}