pseudo: Add may unlink patch

Mark files which are unlinked (nlink == 0) but open with fd's as
"may-unlink" to avoid problematic database entries.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit e1e481f3)
Signed-off-by: Steve Sakoman <steve@sakoman.com>