The difference in behaviour was unfortunate.
The only downside I can see is that this doesn't allow for mixed
origins in the same package, which probably shouldn't be done anyway.
This makes it possible to generate packages that you do not have a
local checkout for, e.g. running:
`gomod2nix generate --outdir example/ golang.org/x/tools/cmd/stringer`
This will be useful for packaging dependencies that you are not
developing, but just simply packaging.
