QPID-5485: By default use a subdirectory of the data dir called "pq" for
page queue files. If neither data dir nor paging dir are set then error
on any attempt to create a paged queue.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1563012 13f79535-47bb-0310-9956-ffa450edef68