HTTPASYNC-75: added setter for NHttpClientEventHandler to HttpAsyncClientBuilder
Contributed by Dmitry Potapov <potapov.d at gmail.com>

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpasyncclient/trunk@1586763 13f79535-47bb-0310-9956-ffa450edef68