WASHINGTON (Reuters) - A U.S. Senate panel advanced a constitutional ban on same-sex marriage on Thursday as the committee chairman shouted "good riddance" to a Democrat who walked out of the tense session."If you want to leave, good riddance," The Senate Judiciary Chairman, Republican Arlen Specter, told Wisconsin Democratic Sen. Russell Feingold, who refused to participate because, he said, the meeting was not sufficiently open to the public."I've enjoyed your lecture too. See you later, Mr. Chairman," Feingold told the Pennsylvania senator before storming out of the private room where the meeting took place. The testy exchange highlighted tensions over...