libctf: failure to open parent dicts that exist should be an error

libctf: failure to open parent dicts that exist should be an error

CTF archive member opening (via ctf_arc_open_by_name, ctf_archive_iter, et
al) attempts to be helpful and auto-open and import any needed parent dict
in the same archive.  But if this fails, the error is not reported but
simply discarded, and you silently get back a dict with no parent, that
*you* suddenly have to remember to import.

This is not helpful behaviour: if the parent is corrupted or we run out of
memory or something, the caller is going to want to know!  Split it in two:
if the dict cites a parent that doesn't exist at all (a lot of historic
dicts name "PARENT" as their parent, even when they're not even children, or
perhaps the parent dict is stored separately and you plan to manually
associate it), we skip it as now, but if the import fails with an actual
error other than ECTF_ARNNAME, return the error and fail the open.

libctf/
	* ctf-archive.c (ctf_arc_import_parent):  Return failure if
        parent opening fails for reasons other thnn nonexistence.
	(ctf_dict_open_sections): Adjust.