minor documentation polish. invalid_bencoding exception isn't used anymore, deprecate it

git-svn-id: http://libtorrent.googlecode.com/svn@10543 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda
fix debug iterator assert

git-svn-id: http://libtorrent.googlecode.com/svn@10544 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda