New names for VC local version backups

[Andre Spiegel]

Stefan and I figured that we need to use a different naming scheme for
automatic version backups (the new mechanism that lets you do local
diffs and reverts).  This is so we can automatically delete them
without interfering with the user.  Thus, these files are no longer
named FILE.~x.y~, as it is done by C-x v ~, but I've rather chosen
FILE.#x.y# for now.  Is that ok with you guys?

The change is installed.  Note that this affects vc-hooks.el, so you
either need to build Emacs anew, or put (load "vc-hooks") into your
.emacs so that it overrides the dumped version of vc-hooks.el.