When pop singer Jason Mraz sang the words “I’m Yours” to a packed house at a rare San Diego club show last week, he was of course speaking as a man to his significant other. Or was he? Perhaps he was taking the perspective of the autographed guitar that said “I’m yours” to the guy in the crowd who bid $11,000 to take it home. Or was it the surfboard that went for $10,000? How about the $8,000 set of three limited-edition Green Day skate decks?Mraz headlined the second-annual benefit concert for the Rob Machado Foundation, a non-profit organization founded by the pro surfer to raise money and a