Tt could be the big showbiz showdown in the Christmas pop charts. In one corner, the "Spice Girls". The self-styled pioneers of Girl Power hope to signal the end of their exile with their record, "Headlines: Friendship Never Ends". In the other corner, "Girls Aloud" - who've seen off all comers since the Spice Girls quit the scene. Their contender - out on Monday - is called "Call The Shots". So, what do they make of the Spices being back on the scene?