* src/files.c (do_lockfile): Check whether the directory
          of the file we're trying to lock exists, and make the
          resulting error message more intuitive.  Fixes
          Savannah bug 42639 by bens.



git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@5056 35c25a1d-7b9e-4130-9fde-d3aeb78583b8