fix bugs in convert_to/from_native() on windows

git-svn-id: http://libtorrent.googlecode.com/svn/trunk@10043 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda
fix windows build error

git-svn-id: http://libtorrent.googlecode.com/svn/trunk@10045 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda