Merge r1749658 from trunk:

Support multiple module dependencies for the final prereq argument to the
APACHE_MODULE macro, as a comma separated list, e.g.

APACHE_MODULE(proxy_http2, [...], [proxy,http2])

will evaluate the availability of mod_proxy, followed by mod_http2

Submitted by: wrowe
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1749773 13f79535-47bb-0310-9956-ffa450edef68