Hi Ben,

thanks for the report.

I've fixed it in a545090ce5e6b9da1f473f558dabda69f317e461 on guix master
by allowing absolute paths as python-cairocffi's dlopen's parameter
and also substituting the sonames by the absolute paths in the callers.

python-cairocffi's dlopen is re-exported.  That means that users that
use it also have to use the absolute paths.