add and use "has_fixup" flag.

add and use "has_fixup" flag.

When we copy an attribute, we need to check if it has pending
fixups.  If so, we can't copy it.  This gives the admin a
descriptive error, rather than having something go wrong later.

This situation happens when we're cloning an attribute that has
children, and those children have fixups.

A more in-depth fix would be to move the fixup lists to the
fr_dict_t.  The cloned attribute could then add itself to a
separate "clone after fixups" list.  So the clone could be applied
last, after all of the fixups have been applied.

Part of the fix is checking for pending fixups and complaining.
More of the fix is setting "ref=..." immediately, if it can be
resolved.  That way we avoid many pending fixups.