When starting a new piped error logger for the main server, ensure

When starting a new piped error logger for the main server, ensure
that the new child's stderr is not a pipe to an old piped logger:

* server/log.c (log_child): Add "dummy_stderr" parameter; if set,
duplicate stdout as the stderr for the child.
(open_error_log): Add "is_main" parameter; use dummy stderr for logger
for main server only.
(ap_open_logs, ap_open_piped_log): Adjust for new open_error_log()/
log_child() parameters.

PR: 40651
Submitted by: jorton, rpluem

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@452431 13f79535-47bb-0310-9956-ffa450edef68