[computer-go] CGOS update

[Don Dailey]

I just made some minor bug fixes and a few very minor enhancements to
the CGOS game server.

If anyone is interested, here are the changes:

      1) changed minimal K factor from 6.0 to 4.0
      2) players "age out" after 32 days.
      3) slighly better valid user name checking.
      4) web site displays number of players logged on.
      5) fixed bug in sorting (negative ratings was broken)

If your bot no longer appears, it will be because it has not logged onto
the server in the last 32 days.   It doesn't have to actually play a
game, it just has to log on to get back on the list.

You also age out very quickly if you have played less than 20 games.

- Don