Use filepath as the last default sort key for pages

hugolib/pageSort.go

@@ -43,6 +43,9 @@ func (by PageBy) Sort(pages Pages) {
 var DefaultPageSort = func(p1, p2 *Page) bool {
 	if p1.Weight == p2.Weight {
 		if p1.Date.Unix() == p2.Date.Unix() {
+			if p1.LinkTitle() == p2.LinkTitle() {
+				return (p1.FullFilePath() < p2.FullFilePath())
+			}
 			return (p1.LinkTitle() < p2.LinkTitle())
 		}
 		return p1.Date.Unix() > p2.Date.Unix()