libctf, archive, link: fix parent importing

libctf, archive, link: fix parent importing

We are about to move to a regime where there are very few things you can do
with most dicts before you ctf_import them.  So emit a warning if
ctf_archive_next()'s convenience ctf_import of parents fails.  Rip out the
buggy code in ctf_link_deduplicating_open_inputs which opened the parent by
hand (with a hardwired name), and instead rely on ctf_archive_next to do it
for us (which also means we don't end up opening it twice, once in
ctf_archive_next, once in ctf_link_deduplicating_open_inputs).

While we're there, arrange to close the inputs we already opened if opening
of some inputs fails, rather than leaking them.  (There are still some leaks
here, so add a comment to remind us to clean them up later.)

libctf/
	* ctf-archive.c (ctf_arc_import_parent): Emit a warning if importing
	fails.
	* ctf-link.c (ctf_link_deduplicating_open_inputs): Rely on the
        ctf_archive_next to open parent dicts.