generate CSS banners via Gruntfile; fixes #10101

Gruntfile.js

@@ -8,7 +8,7 @@ module.exports = function(grunt) {
 
     // Metadata.
     pkg: grunt.file.readJSON('package.json'),
-    banner: '/**\n' +
+    banner: '/*!\n' +
               '* Bootstrap v<%= pkg.version %> by @fat and @mdo\n' +
               '* Copyright <%= grunt.template.today("yyyy") %> <%= pkg.author %>\n' +
               '* Licensed under <%= _.pluck(pkg.licenses, "url").join(", ") %>\n' +
@@ -73,7 +73,8 @@ module.exports = function(grunt) {
 
     recess: {
       options: {
-        compile: true
+        compile: true,
+        banner: '<%= banner %>'
       },
       bootstrap: {
         src: ['less/bootstrap.less'],