In an extraordinary weekend of policy moves, brokerages and fund managers vowed to buy massive amounts of stocks, helped by China’s state-backed margin finance company, which in turn would be aided by a direct line of liquidity from the central bank. Oliver Barron, China policy research analyst at NSBO, said it wasn’t just faith in the markets at stake after investors had ignored official measures to prop up the market as equity indexes slid around 12 percent last week.