libpng: reintroduce 1.5, some pkgs need older

pkgs/development/libraries/libpng/15.nix

@@ -0,0 +1,24 @@
+{ stdenv, fetchurl, zlib }:
+
+assert zlib != null;
+
+stdenv.mkDerivation rec {
+  name = "libpng-1.5.14";
+
+  src = fetchurl {
+    url = "mirror://sourceforge/libpng/${name}.tar.xz";
+    sha256 = "0m3vz3gig7s63zanq5b1dgb5ph12qm0cylw4g4fbxlsq3f74hn8l";
+  };
+
+  propagatedBuildInputs = [ zlib ];
+
+  doCheck = true;
+
+  passthru = { inherit zlib; };
+
+  meta = {
+    description = "The official reference implementation for the PNG file format";
+    homepage = http://www.libpng.org/pub/png/libpng.html;
+    license = "free-non-copyleft"; # http://www.libpng.org/pub/png/src/libpng-LICENSE.txt
+  };
+}

pkgs/top-level/all-packages.nix

@@ -4431,6 +4431,7 @@ let
   libpng = callPackage ../development/libraries/libpng { };
   libpng_apng = callPackage ../development/libraries/libpng/libpng-apng.nix { };
   libpng12 = callPackage ../development/libraries/libpng/12.nix { };
+  libpng15 = callPackage ../development/libraries/libpng/15.nix { };
 
   libpaper = callPackage ../development/libraries/libpaper { };