[syslinux] Scrollbar visibility

[vfaj-q0gm at dea.spamcon.org]

When I added more entries than would fit vertically in a PXE boot
menu (Cobbler's, using menu.c32), I wondered why there wasn't a
scroll bar.  Finally I realized there was one but it didn't look
very different from the existing screen border.  I changed the
color to increase its visibility.

However, it still doesn't give a good visual clue that it IS a
scrollbar.

Would it be possible to add up and down arrows to the top and
bottom of it so it's more obvious what it is?

Probably there are no arrows in the character set but I think
that a caret and a lowercase v would work well enough.