Add a NO_DETACH environment variable to all MPMs that understand

ONE_PROCESS.  This allows Apache to start up without detaching from
the controlling terminal, but also not going into single process mode.
The main purpose of this patch is to make it very easy to debug the
child process startup code.
PR:	2144


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@85970 13f79535-47bb-0310-9956-ffa450edef68