More dir-locals fixes for files.el.

More dir-locals fixes for files.el.

* lisp/files.el (hack-local-variables-confirm, hack-local-variables-filter):
Doc fix (say _which_ directory `dir-name' is).
(hack-dir-local-variables): Fix setting of `dir-name'.
Previous value seems clearly wrong.  Eg put a risky variable in a
dir-locals file, visit a file in a subdirectory, see which directory
it says the risky variables come from.  It should be the one with the
associated directory variables, not the one containing the visited file.