lib/fs: Handle deduplicated files on NTFS (fixes #1845)

These files always have the symlink bit set, because they are reparse
points. Nonetheless they are not symlinks, and Lstat reports a size for
them. We use this fact to disambiguate, and hope fervently that nothing
else matches this description so it comes back to bite us...

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4622

lib/fs/fsfileinfo_unix.go

@@ -0,0 +1,13 @@
+// Copyright (C) 2017 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+// +build !windows
+
+package fs
+
+func (e fsFileInfo) Mode() FileMode {
+	return FileMode(e.FileInfo.Mode())
+}