[server] Add S3 block backend.
[server] Add S3 object backend.
[server] Fix S3 related bugs.

Handle 307 redirect response from S3.
[server] Change config option name for S3 block backend.
[S3] set CURLOPT_NOSIGNAL option.
[S3] Remove a typedef error.
[S3] Remove verbose log messages.
Fix a compilation error.
[S3] Improve error handling.

* Only send up to 80 requests for each CURL connection;
* Retry on network and server errors.
removed msi/README.markdown