Package "app-text/acroread-5.06-r1" now depends on supersed. Acroread itself does not use supersed, it's used only while running the ebuild. The problem is that supersed overwrites sed but sed is part of the default system profile while supersed is not.
supersed will, at some point in the near future, become the default system sed, in fact. however, for now, the dependency has been removed.
