Convert the apr_create_signal_thread to apr_signal_thread. The main

Convert the apr_create_signal_thread to apr_signal_thread.  The main
difference, is that instead of creating a separate thread to listen for
signals, the thread that calls this function does the listening.  Many
platforms have issues when the main thread isn't the thread that is
listening for signals.  Even more platforms complain when the main thread
dies, but the process doesn't.  This gets the main thread back to being
the signal handling thread.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@88831 13f79535-47bb-0310-9956-ffa450edef68