Conflicts/Replaces and dpkg

[Denis Barbier <barbier@imacs.polytechnique.fr>]

I did not read any clear statement on debian-devel about the problem
reported by Josip.

Whatever the solution is, teTeX must be installed after dpkg is
upgraded. So i feel like we could remove the search of old TeX packages
in tetex-*.preinst.

Any comment?

Denis