flac: add test (encode and decode "raw audio")

Here's a test for FLAC. Since the codec is lossless, it's easy to feed it raw data and assert it's the same data after encode+decode.
This method doesn't exist on Ruby 1.8 :( http://bot.brew.sh/job/Homebrew%20Pull%20Requests/18908/version=mountain_lion/testReport/junit/brew-test-bot/mountain_lion/test_flac/