ALBANY — Defense attorneys on Wednesday began their effort to demolish the credibility of Todd Howe, a key prosecution witness in the federal corruption trial of Joe Percoco, former aide to Gov. Andrew Cuomo, and three businessmen who allegedly paid him more than $300,000 in bribes.In a Manhattan federal courtroom Wednesday, Percoco's attorney Barry Bohrer wasted no time in establishing Howe's years of lying to friends and employers, and living well beyond his ample financial means."Mr. Howe, are you an honest man?," Bohrer asked."I am today," he said.