Fix n and N direction independent of search command

By default, n goes in the same direction as the most recent search
command, and N goes in the opposite direction; this is unfortunate
because that means they go in different directions depending on whether
your most recent search was / or ? or * or #.

The problem with the old solution, besides not affecting ?, was that
since it would momentarily search forwards, it could cause the file to
momentarily jump down when doing #. (For example, say 'asdf' appears on
lines 3, 30, and 300, and you're on line 30, and line 30 isn't centered
in the screen; then you do #, it would actually do *, which would jump
to line 300, then jump all the way back to line 3, and since it's
jumping really far, it would center line 3 in your screen; whereas
normally with line 3 and 30 both visible, nothing would scroll or jump.)