back-port shutdown assert fix

git-svn-id: http://libtorrent.googlecode.com/svn@9881 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda
fix to use proxy settings when adding .torrent file from URL

git-svn-id: http://libtorrent.googlecode.com/svn@9882 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda
merged proxy fix for adding .torrent file by URL from RC_0_16

git-svn-id: http://libtorrent.googlecode.com/svn@9883 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda