lookup-cont takes a DFG as its argument

lookup-cont takes a DFG as its argument

* module/language/cps/dfg.scm (lookup-cont): Change to take a DFG
  instead of a cont table.
  (build-cont-table): Change to return a vector.

* module/language/cps/arities.scm:
* module/language/cps/contification.scm:
* module/language/cps/dce.scm:
* module/language/cps/effects-analysis.scm:
* module/language/cps/elide-values.scm:
* module/language/cps/reify-primitives.scm:
* module/language/cps/simplify.scm:
* module/language/cps/slot-allocation.scm: Adapt to lookup-cont and
  build-cont-table changes.