Where httpd fails on startup, users expect an error message to show on stderr. But when a fatal error occurs in a post_config function, all messages including the core's final "Configuration Failed" go only to error_log. The commandline user gets no clue that startup failed. apachectl is also silent. Solution: if something fails at ap_run_post_config, main.c should report on stderr immediately before exit!
Trunk fix in r1533728. Will see if anyone screams before proposing backport.