Use the new APR_POLLSET_NOCOPY option when creating the core pollset.

This eliminates the descriptor copying and mutex operations, and
O(n)-time apr_pollset_remove() loop when used with an apr_pollset
implementation that support the no-copy optimization.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/async-dev@327757 13f79535-47bb-0310-9956-ffa450edef68