说明：  A very simple ftp server s source code for demonstration. * It supports PASV/PORT modes and following operations: * ls,pwd,cwd,get,put,dele. * I have tested it using following ftp clients: * 1. Windows XP s command line ftp client, * 2. IE 6.0, * 3. Redhat 9.0 s ftp client, * 4. CuteFTP 8, * I ll introduce more functions and improve its performance