bus: when we unmarshal an fd it should stay owned by the message object

If the user wants the fd to stay valid he should keep a reference to the
message object or duplicate the fd.

This unifies behaviour of demarshalling data fields and unix fds.
localctl: skip locale entries with non-UTF8 names

glibc should place these in the locale archive. For now, let's just skip
them from our output, since they are aliases anyway.

https://bugs.freedesktop.org/show_bug.cgi?id=63389