Fix duplicate directories entries on metadata change

Currently directory changes are not added to the list of
included directories, allowing those directories to receive
duplicate entries where there is both a metadata change to the
directory and a change to a file under that directory.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

archive/tar.go

@@ -583,6 +583,9 @@ func (cw *changeWriter) includeParents(hdr *tar.Header) error {
 			}
 		}
 	}
+	if hdr.Typeflag == tar.TypeDir {
+		cw.addedDirs[name] = struct{}{}
+	}
 	return nil
 }