propagate a negative score point along breaks/conflicts

propagate a negative score point along breaks/conflicts

versioned -dev packages like db and boost have the problem of no
dependencies which would give them a competitive advantage against an
older incarnation of the -dev package, so they tend to be kept back
until the old version is removed from the archive, which, if the user
has older releases in its sources can take a long time (or never happens).

The newer version has a conflicts/breaks against the older one, but the
older one hasn't against the newer, so by giving via the conflicts the
older one a reduced score the newer one can win if there is no other
reason to keep it. If both have a conflict against each other the
scoring will cancel itself out, so no harm done.

This gives "action" a slightly bigger edge in breaks/conflicts cases
than before, but holding back isn't a really good solution anyway.