Merge r1460185:

    kill the threads in the thread pool in a pre-cleanup
    
    This makes sure that the threads are killed when we start destroying
    any sub-pools they may be using.


git-svn-id: https://svn.apache.org/repos/asf/apr/apr-util/branches/1.5.x@1460278 13f79535-47bb-0310-9956-ffa450edef68