Wall Street is ditching the white stuff in favor of something somewhat more green. And we're not talking about cash. Marijuana was present in 80% of failed drug tests last year, up from 64% in 2007, according to the tests reviewed by Sterling Infosystems Inc.. Cocaine showed up in only 7% of positive Wall Street drug tests last year, instead of 16% in 2007. Relative to the rest of the working world (3.6% of whom failed drug tests last year), the finance industry is pretty clean, with only a 2% rate of drug test failure, according to the Wall Street...