'[[ ! -v "$propagatedOutputs" ]]' is incorrect and always evaluates to
true. The correct form using double brackets would be
'[[ ! -v propagatedOutputs ]]', but I strongly dislike '[[ ]]' due to
the totally different quoting rules compared to everything else in bash.
Now development stuff is propagated from the first output,
and userEnvPkgs from the one with binaries.
Also don't move *.la files (yet). It causes problems, and they're small.
Now it should contain *all* information from stdenv/setup.sh of
the original mutiple-output branch.
However, the configurability of the output paths is much greater.
