Make the Nautilus extension work again.
It was broken since commit 0d1fe255, i.e. in the MAT 0.6 and 0.6.1 releases. The impact is: the MAT extension for Nautilus fails to clean metadata, without making the user aware of it. This bug was discovered by the Tails contributor sajolida, and initially reported to Debian as https://bugs.debian.org/858058.