gradle: reinit at 2.5.

For some projects (especially using android ndk), we still need to keep 2.5.

pkgs/development/tools/build-managers/gradle/2.5.nix

···
+{ stdenv, fetchurl, unzip, jdk, makeWrapper }:
+
+stdenv.mkDerivation rec {
+  name = "gradle-2.5";
+
+  src = fetchurl {
+    url = "http://services.gradle.org/distributions/${name}-bin.zip";
+    sha256 = "0mc5lf6phkncx77r0papzmfvyiqm0y26x50ipvmzkcsbn463x59z";
+  };
+
+  installPhase = ''
+    mkdir -pv $out/gradle
+    cp -rv lib $out/gradle
+
+    gradle_launcher_jar=$(echo $out/gradle/lib/gradle-launcher-*.jar)
+    test -f $gradle_launcher_jar
+    makeWrapper ${jdk}/bin/java $out/bin/gradle \
+      --set JAVA_HOME ${jdk} \
+      --add-flags "-classpath $gradle_launcher_jar org.gradle.launcher.GradleMain"
+  '';
+
+  phases = "unpackPhase installPhase";
+
+  buildInputs = [ unzip jdk makeWrapper ];
+
+  meta = {
+    description = "Enterprise-grade build system";
+    longDescription = ''
+      Gradle is a build system which offers you ease, power and freedom.
+      You can choose the balance for yourself. It has powerful multi-project
+      build support. It has a layer on top of Ivy that provides a 
+      build-by-convention integration for Ivy. It gives you always the choice
+      between the flexibility of Ant and the convenience of a 
+      build-by-convention behavior.
+    '';
+    homepage = http://www.gradle.org/;
+    license = stdenv.lib.licenses.asl20;
+  };
+}

pkgs/top-level/all-packages.nix

···
 
   gradle = callPackage ../development/tools/build-managers/gradle { };
 
+  gradle25 = callPackage ../development/tools/build-managers/gradle/2.5.nix { };
+
   gperf = callPackage ../development/tools/misc/gperf { };
 
   grail = callPackage ../development/libraries/grail { };