WebDAV on Debian unstable cannot handle renames on WebDAV from
file.ext to newfile (without ext) when newfile* already
exists. Normally, git creates a file like 'objects/xx/sha1.token',
which is renamed to 'objects/xx/sha1' when transferred completely.

Just use '_' instead of '.' so WebDAV doesn't see it as an extension
change.
Signed-off-by: NRutger Nijlunsing <git@tux.tmfweb.nl>
Acked-by: NJohannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: NJunio C Hamano <junkio@cox.net>