back ported bitfield test from libtorrent_aio

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@9458 a83610d8-ad2a-0410-a6ab-fc0612d85776
regenerate html

git-svn-id: https://svn.code.sf.net/p/libtorrent/code/trunk@9460 a83610d8-ad2a-0410-a6ab-fc0612d85776