Proposal: deepseq should not depend on containers

Ticket: http://hackage.haskell.org/trac/ghc/ticket/4868 Copy of proposal: The deepseq package depends on the containers package. This forces all packages that want to depend on deepseq in order to provide a NFData instance for exported types, to also depend on containers. Proposal, have containers depend on deepseq, not the other way around, and define the NFData instances for the types in the containers package, in the containers package. Discussion deadline: 2 weeks.