code: private boolean isSealed(String name, Manifest man)
      {
          String path = name.replace('.', '/').concat("/");
          Attributes attr = man.getAttributes(path);
          String sealed = null;
          if (attr != null) {
              sealed = attr.getValue(Name.SEALED);
          }
          if (sealed == null) {
              if ((attr = man.getMainAttributes()) != null) {
                  sealed = attr.getValue(Name.SEALED);
              }
          }
          return "true".equalsIgnoreCase(sealed);
      }
docs: returns true if the specified package name is sealed according to the given manifest.