Support delete command-element form current position.
Fix bug of: command: sysname STRING<1-24>, with "ctrl + w", #1
Fix the bug: 命令行不完整时，错误命令定位位置错误;
Add new command: guet/hdu judge ip port.
Add new command: set hdu/guet accout & password
修复分布式vjudge时，会先被本地主judger先判为skipped的问题