Update list, listout for two‐stage builds

`make list` and `make listout` now list files from both stages. Note
that in the case of `make listout`, these files may be in _either_
`/build/stage1/public/` or `/build/stage2/public/` (but hopefully not
both).

`list1`, `list2`, `listout1`, and `listout2` are added to list files
just from a particular stage.