separate out TORRENT_EXPORT from config.hpp for ed25519 build

git-svn-id: http://libtorrent.googlecode.com/svn@10147 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda
merged change from RC_1_0

git-svn-id: http://libtorrent.googlecode.com/svn@10148 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda
fix build and suppress offsetof warnings in backwards-compatibility code

git-svn-id: http://libtorrent.googlecode.com/svn@10149 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda