Fix: trying to overwrite '/etc/vim/vimrc', which is also in package vim-common 2:7.3.547-7

This is a Replaces without Conflicts+Provides, which tells dpkg to
just go on and overwrite the file and that yes, this is no accident.

(That being said, replacing conffiles is tricky.)

Nevertheless, this makes grml-etc-core installable on wheezy.