include git revision in assets/ dir (.gitignore it)

Makes it easier to see what's been built into an apk if the file's name
has changed.

xwords4/android/.gitignore

@@ -5,4 +5,4 @@ XWords4-gcm/
 **.iml
 local.properties
 .idea
-
+app/src/main/assets/build-info.txt

xwords4/android/app/build.gradle

@@ -232,25 +232,13 @@ task cleanNDK(type: Exec) {
     commandLine lst
 }
 
-// def getVersionName() {
-//     try {
-//         def stdout = new ByteArrayOutputStream()
-//         exec {
-//             commandLine 'git', 'describe', '--dirty'
-//             standardOutput = stdout
-//         }
-//         return stdout.toString().trim()
-//     }
-//     catch (ignored) {
-//         return null;
-//     }
-// }
+task makeBuildAssets() {
+    def assetsDir = android.sourceSets.main.assets.srcDirs.toArray()[0]
+    String path = new File(assetsDir, 'build-info.txt').getAbsolutePath()
+    File file = new File(path);
+    file.write("git: ${GITREV}\n");
+}
 
-// def renameArtifact(variant) {
-//     variant.outputs.each { output ->
-//         def name = String.format( "XWords4-%s-%s.apk", variant.name,
-//                                   getVersionName() )
-//         output.outputFile = new File( (String)output.outputFile.parent, 
-//                                       (String)name )
-//     }
-// }
+gradle.projectsEvaluated {
+    build.dependsOn(makeBuildAssets)
+}