stdenv: Store one package per line in nix-support/propagated-*

This makes those files a bit easier to read. Also, for what it's worth,
it brings us one baby step closer to handling spaces in store paths.

Also, I optimized handling of many transitive deps with read. Probably,
not very beneficial, but nice to enforce the pkg-per-line structure.
Doing so let me find much dubious code and fix it.

Two misc notes:

 - `propagated-user-env-packages` also needed to be adjusted as
   sometimes it is copied to/from the propagated input files.

 - `local fd` should ensure that file descriptors aren't clobbered
   during recursion.

pkgs/development/haskell-modules/generic-builder.nix

@@ -311,7 +311,7 @@ stdenv.mkDerivation ({
     ${optionalString isGhcjs ''
       for exeDir in "$out/bin/"*.jsexe; do
         exe="''${exeDir%.jsexe}"
-        printf '%s\n' '#!${nodejs}/bin/node' > "$exe"
+        printLines '#!${nodejs}/bin/node' > "$exe"
         cat "$exeDir/all.js" >> "$exe"
         chmod +x "$exe"
       done