revert: access status fields by name rather than index For better readability.

subrepo: remove "_getstorehashcachepath" referred by no other code paths

subrepo: replace direct file APIs around "writelines" by "vfs.writelines" This patch also replaces "self._getstorehashcachepath" (building absolute path up) by "self._getstorehashcachename" (building relative path up), because "vfs.writelines" requires relative path.