Major source layout change: Moved FTP code into servers/, clients/, and ftp/.

Major source layout change: Moved FTP code into servers/, clients/, and ftp/.

  src/servers/FtpServer.*   # new FTP server, relaying FTP
  src/servers/HttpServer.*  # old ConnStateData parts conflicting w/ FtpServer
  src/clients/FtpClient.*   # code shared by old and new FTP clients
  src/clients/FtpGateway.*  # old FTP client, translating back to HTTP
  src/clients/FtpNative.*   # new FTP client, relaying FTP
  src/ftp/*                 # FTP stuff shared by clients and servers

This change attempts to preserve code in moved files to the extent possible:
Only copied or added code was polished. Future changes will polish moved code.

Unfortunately, bzr does not track code changes across file splits, so the code
moved from ConnStateData (client_side.cc) into HttpServer and FtpServer
classes appears as removed and added in bzr diff. If you want to see the
branch log for the FtpServer or HttpServer code added in this revision, look
in the previous branch revision of client_side.cc.