Citigroup is the latest US bank to see an improvement in its performance as it has reported its first quarterly net profit in almost two years.   "We had our best overall quarter since the second quarter of 2007," chief executive Vikram Pandit said.  The bank made a profit of $1.6 billion compared to a loss of $5.1 billion a year earlier, and revenues rose 99 percent to $24.8 billion.   However, once dividend payments to preferred shareholders were taken into account, it suffered a near-$1bn loss.