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/compilers/openjdk/7.nix

@@ -190,7 +190,7 @@ let
       # any package that depends on the JRE has $CLASSPATH set up
       # properly.
       mkdir -p $jre/nix-support
-      echo -n "${setJavaClassPath}" > $jre/nix-support/propagated-native-build-inputs
+      printLines ${setJavaClassPath} > $jre/nix-support/propagated-native-build-inputs
 
       # Set JAVA_HOME automatically.
       mkdir -p $out/nix-support

pkgs/development/compilers/openjdk/8.nix

@@ -202,7 +202,7 @@ let
       # any package that depends on the JRE has $CLASSPATH set up
       # properly.
       mkdir -p $jre/nix-support
-      echo -n "${setJavaClassPath}" > $jre/nix-support/propagated-native-build-inputs
+      printLines ${setJavaClassPath} > $jre/nix-support/propagated-native-build-inputs
 
       # Set JAVA_HOME automatically.
       mkdir -p $out/nix-support