code: public synchronized void prepend(String k, String v) {
          grow();
          for (int i = nkeys; i > 0; i--) {
              keys[i] = keys[i-1];
              values[i] = values[i-1];
          }
          keys[0] = k;
          values[0] = v;
          nkeys++;
      }
docs: Prepends a key value pair to the beginning of the
  header.  Duplicates are allowed