test: Update mail corpus with original mails (with attachments).

test: Update mail corpus with original mails (with attachments).

The original mails used to pupulate the mail corpus had had their
attachments (obnoxiously) scrubbed by the pipermail mail archiver.
Since we actually want to test the handling of attachments, this is
less than useful. Restore these files from my own collection, (with
some Received and similar headers pruned).