Changing SONAME in library version

[debian-devel@liska.ath.cx (Olе Streicher)]

Dear mentors,

I am the maintainer of the package "cpl". Upstream just released a new
version 6.0 and changed the SONAME for the built libraries from 12 to
20. So, the source now builds a package "libcplcore20" instead of
"libcplcore12". There are a few dependencies of other packages from
libcplcore12, which I all maintain myself (esorex and python-cpl).

The problem is now that I get migration excuses like

"out of date on i386: [...], libcplcore12, [...] (from 5.3.1-1)"

which I don't know how to handle. What is the usual way to get rid of
these? 

Best regards

Ole