Bug 10230: Don't limit valid matches to bibs

The patch for bug 9523 added a JOIN to the biblio table when identifying
the best match so that if a matched record had been deleted it would
not hold up the import process. Unfortunately, this broke all authority
matching, since of course authorities don't appear in the biblio table.
This patch adds a join to auth_header as well, and decides which to
check based on the record type.