fix client timed out bug.
should not return 500 when client timed out.
bugfix

1. 当读文件请求返回status_msg时（如ds正在升级不能提供服务时）仍使用read_resp_msg去解析会导致解析错误，打印错误的内存数据到log中，并可能导致超时
2. 修改默认的从后端接收buf大小为2M，确保在下载文件返回应答的头时能够获得file_info
3. 在下载原生文件时如果得到了文件的file_info，就在应答头里面加上文件的last-modified时间
4. 修复一些错误的返回值
modify GMT time format from UTC+0800 to GMT
1. fix read corrupted large file bug.
2. remove some redundant code.
increased the size of error string to 4096 bytes
Merge pull request #186 from zhuzhaoyuan/errstr-size

Increase the size of the error string to 4096 bytes
Merge pull request #180 from zhcn381/master

nginx-tfs module bugfix
merge changes between nginx 1.2.6 and nginx 1.2.7
added the copyright of NetEase

The upstream check module was developed in NetEase.
Thanks to Netease corpration supporting the opensource modules.
changed the github url of this repository in the README
Merge pull request #189 from yaoweibin/netease

Netease
Merge pull request #188 from cfsego/calibaba

merge changes between nginx 1.2.6 and nginx 1.2.7
updated the README
Merge pull request #193 from zhuzhaoyuan/update-readme2

updated the README