Do not rewrite /etc/default/varnish on upgrade
Do not rewrite /etc/default/varnish on upgrade

 - This introduced a bug where user was asked about modified configuration
   files where the user had not modified them.

Closes: 698577
Thanks: Andreas Beckmann <6a67b89c45772a3e34a2045a2631c0b9ed72f211@debian.org>

ssm/pkg-varnish,ssm/pkg-varnish,ssm/pkg-varnish,ssm/pkg-varnish,ssm/pkg-varnish