By Marc Jones LONDON (Reuters) - World shares extended gains on Tuesday, tracking a rally on Wall Street spurred by a good start to the U.S. earnings season that put the gloss on last week's strong job data, while the dollar held near multi-year peaks. European shares on the broad FTSEurofirst 300 opened up 0.6 percent and core and peripheral euro zone debt made early gains as a deal to drip-feed Greece the latest 6.8 billion euro installment of its bailout added to the upbeat mood. ...