Changes with nginx 1.2.8 02 Apr 2013

*) 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.