By Tom Bryant Tell you what we want, what we really, really want… it’s whatever Posh was having at her fabulous 50th birthday party (tequila, apparently). And what a party it was: Tom Cruise doing the splits on the dancefloor; all five Spice Girls reuniting for a sing-song; and the birthday girl welling up as all of her children and husband David gave moving speeches in her honour. No wonder Posh was looking, well, a bit tired and emotional as Becks gave her a piggy back out of the party at Oswald’s in Mayfair, before bundling her into the back of the car. Still, it was a night to remember –…