* Abbott 2013 profit forecast slightly above Street view * Humira sales growth a good sign for AbbVie * Abbott shares slip; AbbVie shares rise 3.8 percent By Ransdell Pierson Jan 23 (Reuters) - AbbVie Inc, the new branded pharmaceuticals company spun off by Abbott Laboratories Inc , is off to a good start, judging by fourth-quarter sales of arthritis drug Humira and other products in its medicine chest.