vfs: add symlink support to VFS

This is somewhat limited in that it only resolves symlinks when files
are opened. This will work fine for the intended use in rclone mount,
but is inadequate for the other servers probably.

vfs/write.go

@@ -37,6 +37,9 @@ var (
 )
 
 func newWriteFileHandle(d *Dir, f *File, remote string, flags int) (*WriteFileHandle, error) {
+	if f.IsSymlink() {
+		remote += fs.LinkSuffix
+	}
 	fh := &WriteFileHandle{
 		remote: remote,
 		flags:  flags,