build(gulp): watch and incrementally compile files for server.js.dev task

Closes angular#1770

Author: IgorMinar

gulpfile.js

@@ -225,10 +225,17 @@ gulp.task('build/checkCircularDependencies', function (done) {
 
 // ------------------
 // web servers
-gulp.task('serve.js.dev', jsserve(gulp, gulpPlugins, {
-  path: CONFIG.dest.js.dev.es5,
-  port: 8000
-}));
+gulp.task('serve.js.dev', ['build.js.dev'], function(neverDone) {
+  watch('modules/**', function() {
+    gulp.start('!broccoli.js.dev');
+  });
+
+  jsserve(gulp, gulpPlugins, {
+    path: CONFIG.dest.js.dev.es5,
+    port: 8000
+  })();
+});
+
 
 gulp.task('serve.js.prod', jsserve(gulp, gulpPlugins, {
   path: CONFIG.dest.js.prod.es5,