prefork in ONE_PROCESS mode:

child_main() called clean_child_exit() in almost all paths,
and returned to the caller in one infrequent path; just
call clean_child_exit() always


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1076454 13f79535-47bb-0310-9956-ffa450edef68