There are two aspects to this change.

The uncontroversial one is that if the install plan contains
reinstalls, we now determine if there are reverse dependencies
of such reinstalled packages that we can see. If so, these
are likely to be broken. If we find such packages, we list
them and state that we can only install the plan if
--force-reinstalls is explicitly stated.

The more controversial change is that if we cannot find such
reverse dependencies, we now merely print a warning but
continue, even though there are situations where executing
the build process can still break packages. The most likely
example of this is that we're installing to the global package
database, and user package databases on the system have
dependencies on the replaces packages -- but we cannot see
these user package databases.