Add missing language attributes to programlisting tags for highlighting.

docs/docs.gradle

@@ -1,4 +1,4 @@
-// Docbook and Javadoc building and uploading tasks
+    // Docbook and Javadoc building and uploading tasks
 apply plugin: 'base'
 
 task docs {
@@ -47,6 +47,12 @@ project('manual') {
     }
 }
 
+task reference (type: Copy) {
+    dependsOn 'manual:docbook'
+    destinationDir = buildDir
+    with(project('manual').spec)
+}
+
 task apidocs(type: Javadoc) {
     destinationDir = new File(buildDir, 'apidocs')
     title = "Spring Security $version API"