Let's face it, there's always been plenty of extra work to be done at Christmas time. Be it late night shelf-stacking at your local mall, cramming this year's must-have items into valuable shop space in an effort to fuel the 'pile 'em high, sell 'em dear' festive shopping frenzy, or doing the night shift down the sorting office to help out the postie, it's a tradition for students, down-at-pocket teenagers and lonely housewives.But the seasonal labour market hasn't always been just about earning pin money and having a lark. Back in the olden days, folks had to work their fingers to the bone in some of the worst Christmas jobs in history …