TimestampUtils.toString() speedup

Here is a small change that improved the performance of setting a timestamp field on a prepared statement from 0.513ms to 0.083ms in our tests.  Measured using JProfiler for 50,000 iterations. Essentially it is switching to use SimpleDateFormat for toString().  I believe this code is from the 8.1 408 driver.

    public static final SimpleDateFormat pgdtf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ssZ GG");
    private static final FieldPosition FIRSTPOS = new FieldPosition(0);
   
    public synchronized String toString(Calendar cal, Timestamp x) {
        if (cal == null)
            cal = defaultCal;

        cal.setTime(x);
        sbuf.setLength(0);

        if (x.getTime() == PGStatement.DATE_POSITIVE_INFINITY) {
            sbuf.append("infinity");
        } else if (x.getTime() == PGStatement.DATE_NEGATIVE_INFINITY) {
            sbuf.append("-infinity");
        } else {

            pgdtf.format(cal.getTime(), sbuf, FIRSTPOS);

            /*
            appendDate(sbuf, cal);
            sbuf.append(' ');
            appendTime(sbuf, cal, x.getNanos());
            appendTimeZone(sbuf, cal);
            appendEra(sbuf, cal);
            */
        }

        showString("timestamp", cal, x, sbuf.toString());
        return sbuf.toString();
    }