Richard H. Donohue can’t quite put his finger on it. After the state legislature rapidly approved a cut to the number of jurors in state civil cases this week, the defense lawyer and founding partner at Donohue, Brown, Mathewson & Smyth LLC was still trying to pinpoint why the plaintiff bar pushed it so vigorously. “I would love to know what the plaintiffs’ lawyers have up their sleeve on this,” Donohue said today, referring to the bill that surfaced the day before Thanksgiving and couples a …