Previously the hook system would only allow extensions of ".service"
and ".timer". Any other name would have ".service" appended.
Now the hook system allows any suffix listed at
https://www.freedesktop.org/software/systemd/man/systemd.unit.html.
If no suffix is found, ".service" is still added to preserve backwards-
compatibility.
Note that backwards-compatibility may still break for users relying on
the previous behavior in odd ways. For example, a hook with name
"my-hook.slice" would previously have been installed as
"my-hook.slice.service", but it will now be installed as "my-hook.slice",
since ".slice" is a valid systemd unit file extension.
mooncake
Matt Dougherty