move loadDownloadState to init
新V4下载策略整合进FBT
fix bug: randomAccessFile
global.log.info => fs.write
add partdownload resend, timeout=10s
fix bug: filesize undefined
fix bug: randomaccessfile out of bound
www->dev
download part setTimeOut->setTimeInterval
fix bug: res_hash doesn't have size field
fix bug: e.emit("got response")
完善socket已被关闭的错误处理, resend最初的延时变成5倍interval
延时统一为10s