The file is moved into a new "include-private" directory. This is done
because otherwise adjustments would have to be made to the list of installed
headers, the way include tests currently work and which files are
used for generating documentation.
This function sends a DBusMessage on a DBusConnection
and sets the reply callback of the resulting DBusPendingCall,
as well as properly cancelling the pending call if anything fails.
It is inherently racy, and we have a better way to ensure that
we won't autostart the service:
dbus_message_set_auto_start()
So use that.
This commit also adds a missing call to `dbus_pending_call_unref()`
and indirectly fixes a type mismatch (`dbus_bool_t` vs. `bool`)
that was present in `is_dbus_service_running()`.