add more utp statistics and make the congestion controller less aggressive when the up-link is not saturated

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@8940 a83610d8-ad2a-0410-a6ab-fc0612d85776
don't count pad-files as partial download pieces in the piece picker. prioritize which immutable dht items to keep also based on distance from our ID. remove some todo comments that probably should not be done

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@8941 a83610d8-ad2a-0410-a6ab-fc0612d85776
include error code in metadata failure alert

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@8942 a83610d8-ad2a-0410-a6ab-fc0612d85776
merged build fix without exceptions from RC_0_16

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@8944 a83610d8-ad2a-0410-a6ab-fc0612d85776
when evicting peers waiting to establish connection, evict the ones that have been trying for the longest first

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@8945 a83610d8-ad2a-0410-a6ab-fc0612d85776
improve DHT routing table some, by replacing high RTT nodes within a node ID prefix

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@8946 a83610d8-ad2a-0410-a6ab-fc0612d85776
make verbose dht logging work again

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@8947 a83610d8-ad2a-0410-a6ab-fc0612d85776
fix stats logging

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@8950 a83610d8-ad2a-0410-a6ab-fc0612d85776