forcing a package update after an OS update

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

I upgraded a machine to a new NetBSD version and now pkg_add refuses to 
update the installed packages because the same version is already installed. 
It is, but for the former NetBSD version. Most prominently, pkg_install 
itself is affected, so the solution isn't "just pkg_delete before".
The packages mostly work, but I would rather install the new versions.
Any option to pkg_install to force the update?