pkg/archive.statDifferent(): care about mtime for directories

When considering changes, don't ignore differences between directories
when their mtimes are the only thing we check that's changed.  This
creates a difference in behavior between the vfs and overlay drivers
that shows up in build conformance tests.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

pkg/archive/changes_unix.go

@@ -31,9 +31,9 @@ func statDifferent(oldStat *system.StatT, oldInfo *FileInfo, newStat *system.Sta
 		ownerChanged ||
 		oldStat.Rdev() != newStat.Rdev() ||
 		oldStat.Flags() != newStat.Flags() ||
+		!sameFsTimeSpec(oldStat.Mtim(), newStat.Mtim()) ||
 		// Don't look at size for dirs, its not a good measure of change
-		(oldStat.Mode()&unix.S_IFDIR != unix.S_IFDIR &&
-			(!sameFsTimeSpec(oldStat.Mtim(), newStat.Mtim()) || (oldStat.Size() != newStat.Size()))) {
+		(!sameFsTimeSpec(oldStat.Mtim(), newStat.Mtim()) || (oldStat.Size() != newStat.Size())) {
 		return true
 	}
 	return false