Fix crash accessing pollset on worker thread when child process is exiting.

Fix crash accessing pollset on worker thread when child process is exiting.

The timeout mutex and pollset were allocated from the listener thread
pool.  During child process shutdown, the listener thread exits first
while any outstanding requests finish.  These objects need to be allocated
from pchild since the lifetime extends until the last worker thread has
finished.

Switch to pchild, and move init of these objects to the same place as
other thread-independent objects.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1000814 13f79535-47bb-0310-9956-ffa450edef68