WASHINGTON — President Barack Obama had a blunt status update for America's permanently wired youth on Tuesday: your Facebook postings could come back to haunt you. Obama's advice to a group of high school students followed reports that prospective employers may be mining social networking sights for background information on job applicants. He offered his nugget of advice to a student at an Arlington, Virginia school who asked him in a roundtable how he could get to be president. "First of all, I want everybody here to be careful about what you post on Facebook, because in the YouTube age...