Since systemd moved to /usr/lib, the old /lib/systemd install rule
didn't match anymore. However, the fix in
https://bugs.debian.org/1057421 was actually misguided. It fixed the
"not found error", but it was still wrong. It caused the package to
not compile with old systemd anymore (don't ask why I needed to
compile for that).

The fix missed the fact that a .sleep file was installed into
systemdsleepdir (as mentioned in configure.ac line 58) while other
systemd files end up in systemdsystemunitdir. This was missed because
with a new systemd *all* systemd files are actually caught by the /usr
install rule right below the changed line from the patch in
above-mentioned bug.

Attached, you find a patch that actually fixes the build for both old
and new versions of systemd.

Cheers,
Sven