merged the diff between nginx-1.2.7 and nginx-1.2.8

  
    *) Bugfix: new sessions were not always stored if the "ssl_session_cache
       shared" directive was used and there was no free space in shared
       memory.
       Thanks to Piotr Sikora.

    *) Bugfix: responses might hang if subrequests were used and a DNS error
       happened during subrequest processing.
       Thanks to Lanshun Zhou.

    *) Bugfix: in the ngx_http_mp4_module.
       Thanks to Gernot Vormayr.

    *) Bugfix: in backend usage accounting.