Switch from private FastCGI protocol handling to util_fcgi API.


Use apr_socket_timeout_get instead of hard-coded 30 seconds timeout.


Bring some envvar flexibility from mod_authnz_fcgi to mod_proxy_fcgi:

mod_proxy_fcgi: Remove 64K limit on encoded length of all envvars.
An individual envvar with an encoded length of more than 16K will be
omitted.


Borrow a fix from mod_authnz_fcgi:

mod_proxy_fcgi: Handle reading protocol data that is split between
packets.


Use ap_log_rdata() to dump the FastCGI header, axing a bunch
of custom data dumping code.

Submitted by: trawick, jkaluza, trawick, trawick, trawick
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1542330 13f79535-47bb-0310-9956-ffa450edef68