add at since tag for new method

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@278144 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/taskdefs/Zip.java

@@ -1390,6 +1390,7 @@ public class Zip extends MatchingTask {
         }
         /**
          * find out if there are absolutely no resources to add
+         * @since Ant 1.6.3
          * @return true if there are no resources to add
          */
         public boolean isWithoutAnyResources() {