Reuters / Richard BrianPsst... there's a fortune to be made buying closed-end funds (CEFs). Just don't tell Wall Street. That was the message delivered in a recent interview by famed credit trader Boaz Weinstein, whose $1.7 billion firm Saba Capital is best known for its winning bet against the JPMorgan trader known as the "London Whale." CEFs, which raise money through initial public offerings and then trade on public exchanges, just like stocks, total $240 billion in market value right now.