normal messages along with voting data (polls, ballots, etc.) would always be
imported in this order: msgs, polls, ballots/votes, and then poll-closures.
This could result in a confusing order of messages in the local msg base where
there were messages in reply to a poll before the poll appears and other
oddities. Anyway, this is now resolved by placing a msg "header block" for each
vote-data item in the MESSAGES.DAT file. Since there is no body/text blocks,
it should be ignored under normal circumstances, but these header blocks are
only created if VOTING.DAT is enabled anyway.
And now, the VOTING.DAT contains an extra line (empty .ini section) with the
HEADERS.DAT offset associated with the chronology of the item. The format
is still backwards compatible with the earlier builds that included VOTING.DAT
support.

Also, fixed the vote/poll/closure Message-IDs containing a msg number of 0
(while not technically a problem, it wasn't the intention) with the use of the
new function: get_new_msg_number().