improve robustness of web_seed unit tests

git-svn-id: http://libtorrent.googlecode.com/svn/trunk@9797 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda
merged i2p_alert fix from RC_0_16

git-svn-id: http://libtorrent.googlecode.com/svn/trunk@9800 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda
fix assert by only constructing piece_block with verified values

git-svn-id: http://libtorrent.googlecode.com/svn/trunk@9801 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda