Incremental search does not match strings that span a
visible/invisible boundary. This results in failure to correctly
isearch for authors in `notmuch-search' mode if the name of the author
is split between the visible and invisible components of the authors
string. To avoid this, attempt to truncate the visible component of
the authors string on a boundary between authors, such that the
entirety of an author's name is either visible or invisible.
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).
