So the weekend press story that the Marks & Spencer (MKS) chief financial officer Humphrey Singer was set to resign has been confirmed this morning. Naturally it is all nice words ('I feel privileged to be a part of the challenging but hugely rewarding turnaround at Marks & Spencer') but let's face it, no CFO exits into the night if something is about to go hugely right – especially after some well-publicised tough times…