Merge 'staging' into closure-size

- there were many easy merge conflicts
- cc-wrapper needed nontrivial changes

Many other problems might've been created by interaction of the branches,
but stdenv and a few other packages build fine now.

pkgs/development/libraries/zlib/default.nix

@@ -2,7 +2,7 @@
 
 let version = "1.2.8"; in
 
-stdenv.mkDerivation rec {
+stdenv.mkDerivation (rec {
   name = "zlib-${version}";
 
   src = fetchurl {
@@ -55,4 +55,13 @@ stdenv.mkDerivation rec {
     description = "Lossless data-compression library";
     license = licenses.zlib;
   };
-}
+} // (if stdenv.isDarwin then {
+  postInstall = ''
+    # jww (2015-01-06): Sometimes this library install as a .so, even on
+    # Darwin; others time it installs as a .dylib.  I haven't yet figured out
+    # what causes this difference.
+    for file in $out/lib/*.so* $out/lib/*.dylib* ; do
+      install_name_tool -id "$file" $file
+    done
+  '';
+} else {}))