Changes with nginx 0.5.18 19 Apr 2007

    *) Feature: the ngx_http_sub_filter_module.

    *) Feature: the "$upstream_http_..." variables.

    *) Feature: now the $upstream_status and $upstream_response_time
       variables keep data about all upstreams before X-Accel-Redirect.

    *) Bugfix: a segmentation fault occurred in master process after first
       reconfiguration and receiving any signal if nginx was built with
       ngx_http_perl_module and perl did not support multiplicity; bug
       appeared in 0.5.9.

    *) Bugfix: if perl did not support multiplicity, then after
       reconfiguration perl code did not work; bug appeared in 0.3.38.