make dht test program able to get and put mutable items. fixed some DHT bugs along the mutable put/get path

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@9750 a83610d8-ad2a-0410-a6ab-fc0612d85776
update dht unit test

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@9751 a83610d8-ad2a-0410-a6ab-fc0612d85776