MountInfo does not unescape special characters

[tatref]

See unmangle_octal function in PR #261

To test:

mkdir "$(echo -e 'aaa\\b\tc\nd#e')"
dd if=/dev/zero bs=1M count=200 of=ext4.img
mkfs.ext4 ext4.img
sudo mount  ext4.img aaa*

Then run example mountinfo, this will give:

/dev/loop0 on /root/test/aaa\134b\011c\012d#e type ext4 (relatime,rw,seclabel)