Typo.
Fixed post_action to not trigger "header already sent" alert.

The alert was introduced in 03ff14058272 (1.5.4), and was triggered on each
post_action invocation.

There is no real need to call header filters in case of post_action,
so return NGX_OK from ngx_http_send_header() if r->post_action is set.
Write filter: fixed handling of sync bufs (ticket #132).
Access log: restricted "log_format" to "http" level.

Specifying the "log_format" directive on levels other than "http"
is deprecated since 73d37e1ccb91 (1.1.11).
Upstream: improved subrequest logging.

To ensure proper logging make sure to set current_request in all event
handlers, including resolve, ssl handshake, cache lock wait timer and
aio read handlers.  A macro ngx_http_set_log_request() introduced to
simplify this.
Cache: proper wakeup of subrequests.

In case of a cache lock timeout and in the aio handler we now call
r->write_event_handler() instead of a connection write handler,
to make sure to run appropriate subrequest.  Previous code failed to run
inactive subrequests and hence resulted in suboptimal behaviour, see
report by Yichun Zhang:

http://mailman.nginx.org/pipermail/nginx-devel/2013-October/004435.html

(Infinite hang claimed in the report seems impossible without 3rd party
modules, as subrequests will be eventually woken up by the postpone filter.)
Trailing spaces removed, typo fixed.
nginx-1.7.8-RELEASE
release-1.7.8 tag