The chairman of Alliance Trust Karin Forseke is to step down in a month's time following this year's bruising battle with major shareholder Elliott Advisers.    Alastair Kerr, the senior independent director and chair of the remuneration committee, is also going at the end of December, several months earlier than expected.  Ms Forseke took over after Alliance saw off its previous activist shareholder challenge in 2012.  This year the board was forced in April into accepting two new non-executives nominated by Elliott, after Ms Forseke had campaigned against them, then last month it announced a complete overhaul of Alliance's governance which saw high-profile chief executive Katherine Garrett-Cox moved off the board.