BEIJING/SAN FRANCISCO (Reuters) – Alibaba is taking a tougher line against counterfeit items sold on its online marketplaces as the Chinese e-commerce giant heads towards a U.S. stock listing that could be the world’s biggest technology company IPO. Some security experts say the Chinese group’s stricter standards on piracy and fake goods may even surpass those of Amazon.com Inc and eBay Inc. In its IPO filing last week, Alibaba Group Holding Ltd said the perception that its sites are cluttered with counterfeit items could hurt its ability to win over customers, investors and U.S.