When taking out all locks on a FSFS repo, don't auto-create lock files
that are not supported / used by the respective repo format.

This is not strictly a correctness fix as the old formats will simply
ignore / not access those lock files.  However, we don't want to litter
the repo with unsupported files.

* subversion/libsvn_fs_fs/fs_fs.c
  (svn_fs_fs__with_all_locks): The txn-current-lock is not always available.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1589252 13f79535-47bb-0310-9956-ffa450edef68