Fix Autoupdate logging users out.

Webwork only allows 1 session per user. When the auto-update runs, it logs in
with the course professor's credentials. This ends up inadvertently logging
professors out of the webwork every hour.

Fixed by switching to the 'admin' user when we run auto-update.

Also discovered that unicode characters in user's first or last names aren't
being stored correctly during course update. It seems that they're being
stored in Perl's interal UTF8 representation without being converted
to the binary UTF8 that the database understands. Fixed by doing an explicit
conversion of the data before storing.