Changes with nginx 1.1.8 14 Nov 2011

*) Change: the ngx_http_limit_zone_module was renamed to the
ngx_http_limit_conn_module.

*) Change: the "limit_zone" directive was superseded by the
"limit_conn_zone" directive with a new syntax.

*) Feature: support for multiple "limit_conn" limits on the same level.

*) Feature: the "image_filter_sharpen" directive.

*) Bugfix: a segmentation fault might occur in a worker process if
resolver got a big DNS response.
Thanks to Ben Hawkes.

*) Bugfix: in cache key calculation if internal MD5 implementation was
used; the bug had appeared in 1.0.4.

*) Bugfix: the "If-Modified-Since", "If-Range", etc. client request
header lines might be passed to backend while caching; or not passed
without caching if caching was enabled in another part of the
configuration.

*) Bugfix: the module ngx_http_mp4_module sent incorrect
"Content-Length" response header line if the "start" argument was
used.
Thanks to Piotr Sikora.