Remove "experimental" tag from MySQL 4.1+ character set options, and warn users again...

Remove "experimental" tag from MySQL 4.1+ character set options, and warn users against using the "backwards-compatble" mode instead, which, it turns out, is a whole lot worse than any problem we've ever had with the so-called experimental modes. Make mysql5-binary the default. Explain the difference between the two 4.1+ modes.