Weekly Infusional High-Dose Fluorouracil (HD-FU), HD-FU Plus Folinic Acid (HD-FU/FA), or HD-FU/FA Plus Biweekly Cisplatin in Advanced Gastric Cancer: Randomized Phase II Trial 40953 of the European Organisation for Research and Treatment of Cancer Gastrointestinal Group and the Arbeitsgemeinschaft Internistische Onkologie