Add .dir-locals.el.

* .dir-locals.el: New file, to help Emacs users produce better
  changesets.  In particular, prevents automatic copyright year
  updates.

BUG=

Review URL: https://codereview.chromium.org/12687003
Patch from  Andy Wingo <wingo@igalia.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13884 ce2b1a6d-e550-0410-aec6-3dcde31c8c00