Grunt task to tickle version # in platform and polymer builds

--release option will prevent placing git revision at the end

tasks/version-number.js

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2013 The Polymer Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style
+ * license that can be found in the LICENSE file.
+ */
+
+module.exports = function(grunt) {
+  grunt.registerTask('version', 'Update version number for builds', function() {
+    grunt.config.requires('pkg.version');
+    var version = grunt.config('pkg.version');
+    // spit back pkg.version if "release" is true
+    var release = grunt.option('release');
+    var done = this.async();
+
+    function getRevision(callback) {
+      grunt.util.spawn({
+        cmd: 'git',
+        args: ['rev-parse', '--short', 'HEAD']
+      }, callback);
+    }
+
+    if (release) {
+      grunt.config('buildversion', version);
+      done(null);
+    } else {
+      getRevision(function(error, ref) {
+        if (!error) {
+          grunt.config('buildversion', version + '-' + ref);
+        }
+        done(error);
+      });
+    }
+  });
+};