Bug#1089022: usr-is-merged is installed, yet still have unmerged-bin systemd taint

[David Eccles (gringer)]

Just in case this crops up for anyone else... I had this issue 
previously, and attempted a manual merge of /usr/sbin and /usr/bin: 
saving the existing /usr/sbin as /usr/sbin_old, then symlinking 
/usr/sbin to /usr/bin.

Unfortunately, this merge broke the usrmerge checks in udev and systemd. 
The preinst script in the packages have the following check:

     [ "$(readlink -f "$DPKG_ROOT$dir")" = "$DPKG_ROOT/usr$dir" ]

When /usr/sbin is symlinked to /usr/bin, then this check fails:

$ readlink -f /bin
/usr/bin
$ readlink -f /sbin
/usr/bin

I attempted to revert my previous changes, removing the symlink and 
copying over the files named in the old directory. This allowed the new 
udev and systemd packages to install without complaint, but I'm not sure 
if I've broken my system more, or made it less broken as a result of 
what I've done.

Ngā mihi,

  - David Eccles