Merge branch 'js/http-custom-headers'

Update tests for "http.extraHeaders=<header>" to be portable back
to Apache 2.2 (the original depended on <RequireAll/> which is a
more recent feature).

* js/http-custom-headers:
submodule: ensure that -c http.extraheader is heeded
t5551: make the test for extra HTTP headers more robust
tests: adjust the configuration for Apache 2.2

diff --cc t/lib-httpd/apache.conf
Simple merge