LONDON (Reuters) - WM Morrisons shares jumped on Tuesday as traders cited market rumours that the UK supermarket chain could be subject to a takeover approach by U.S. online retail giant Amazon.com Inc .They rose as much as 2.9 percent in midday trade and were up 1.9 percent by 1215 GMT, outperforming their UK peers. The FTSE 100 was up 1.5 percent.Chatter about the rumour was mentioned on the Financial Times' Alphaville markets chatroom. The chatroom moderator said: "There's a mad story going..