Upgrade from 1.15.3 to 1.15.4.

<ChangeLog>

*) Feature: now the "ssl_early_data" directive can be used with OpenSSL.

*) Bugfix: in the ngx_http_uwsgi_module.

Thanks to Chris Caputo.

*) Bugfix: connections with some gRPC backends might not be cached when

using the "keepalive" directive.

*) Bugfix: a socket leak might occur when using the "error_page"

directive to redirect early request processing errors, notably errors
with code 400.

*) Bugfix: the "return" directive did not change the response code when

returning errors if the request was redirected by the "error_page"
directive.

*) Bugfix: standard error pages and responses of the

ngx_http_autoindex_module module used the "bgcolor" attribute, and
might be displayed incorrectly when using custom color settings in
browsers.
Thanks to Nova DasSarma.

*) Change: the logging level of the "no suitable key share" and "no

suitable signature algorithm" SSL errors has been lowered from "crit"
to "info".

</ChangeLog>