All other types exported from install.h should be namespaces like this,
hence namespace InstallInfo the same way.
Also, remove external forward definition of UnitFileScope type.
Previously the specifier calls could only indicate OOM by returning
NULL. With this change they will return negative errno-style error codes
like everything else.
This allows one templated unit to refer to another templated unit
at installation time.
Examples:
> grep WantedBy ~/.config/systemd/user/mpop@.timer
WantedBy=services@%i.target
> srv disable mpop@iit.timer
rm '/home/alxchk/.config/systemd/user/services@iit.target.wants/mpop@iit.timer'
> srv enable mpop@iit.timer
ln -s '/home/alxchk/.config/systemd/user/mpop@.timer' '/home/alxchk/.config/systemd/user/services@iit.target.wants/mpop@iit.timer'
Based-on-patch-by: Oleksii Shevchuk <alxchk@gmail.com>
Lennart Poettering
Zbigniew Jędrzejewski-Szmek