reapply 7309426 (configurable completion) which was removed in 9bef3b3
reapply 7309426 (configurable completion) which was removed in 9bef3b3

commercialhaskell/intero,commercialhaskell/intero,chrisdone/intero,commercialhaskell/intero,chrisdone/intero,chrisdone/intero,chrisdone/ghci-ng,chrisdone/ghci-ng