debian/control: make Conflicts: a Breaks:

I: ddate: conflicts-with-version util-linux (<< 2.24.2-1)
N:
N:    An earlier-than version clause is normally an indication that Breaks
N:    should be used instead of Conflicts. Breaks is a weaker requirement that
N:    provides the package manager more leeway to find a valid upgrade path.
N:    Conflicts should only be used if two packages can never be unpacked at
N:    the same time, or for some situations involving virtual packages (where
N:    a version clause is not appropriate). In particular, when moving files
N:    between packages, use Breaks plus Replaces, not Conflicts plus Replaces.
N:
N:    Refer to Debian Policy Manual section 7.4 (Conflicting binary packages -
N:    Conflicts) for details.
N:
N:    Severity: normal, Certainty: wild-guess
N:
N:    Check: fields, Type: binary, udeb, source