code: public static boolean addDefaultExclude(String s) {
          if (defaultExcludes.indexOf(s) == -1) {
              defaultExcludes.add(s);
              return true;
          }
          return false;
      }
docs: Add a pattern to the default excludes unless it is already a
  default exclude.
  
  @param s   A string to add as an exclude pattern.
  @return    <code>true</code> if the string was added;
  <code>false</code> if it already existed.
  
  @since Ant 1.6