improved support for web seeds that don't support keep-alive

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@9186 a83610d8-ad2a-0410-a6ab-fc0612d85776
test_pex fix

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@9189 a83610d8-ad2a-0410-a6ab-fc0612d85776
fixed uninitialized variable in http_parser (introduced with web seeding improvements)

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@9190 a83610d8-ad2a-0410-a6ab-fc0612d85776
optimize some invariant checks and make test_utp shorted, to complete much faster

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@9191 a83610d8-ad2a-0410-a6ab-fc0612d85776
optimize DHT

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@9192 a83610d8-ad2a-0410-a6ab-fc0612d85776
revert a bad optimization from peer_connection's invariant check

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@9193 a83610d8-ad2a-0410-a6ab-fc0612d85776
make test_torrent cheaper

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@9194 a83610d8-ad2a-0410-a6ab-fc0612d85776
if proxy name server lookup fails, and we're not in anonymous mode, disable the proxy and continue

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@9195 a83610d8-ad2a-0410-a6ab-fc0612d85776