NOTTINGHAM, England, Jan 17 : Arsenal increased their lead at the top of the Premier League table following a scoreless draw with Nottingham Forest on Saturday, but it was a bittersweet result for their manager Mikel Arteta.  Manchester City had earlier slumped to a 2-0 defeat by Manchester United, giving Arsenal the opportunity to open up a nine-point gap, but they could not find the back of the net against Forest.  "We came here to win the game, and again, we haven't managed to do that, and