Optional multiple filename support
Optional multiple filename support

I've had this commit on a branch for 9 months working fine. I'm sick of
switching between master and my branch, so I'm just merging it in as an
option.

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