Upgrade from 1.9.14 to 1.9.15.

<ChangeLog>

*) Bugfix: "recv() failed" errors might occur when using HHVM as a

FastCGI server.

*) Bugfix: when using HTTP/2 and the "limit_req" or "auth_request"

directives a timeout or a "client violated flow control" error might
occur while reading client request body; the bug had appeared in
1.9.14.

*) Workaround: a response might not be shown by some browsers if HTTP/2

was used and client request body was not fully read; the bug had
appeared in 1.9.14.

*) Bugfix: connections might hang when using the "aio threads"

directive.
Thanks to Mindaugas Rasiukevicius.

</ChangeLog>