bug#11063: Window-start in the middle of a line with nhexl-mode

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Date: Wed, 21 Mar 2012 23:23:05 -0400
> 
> % src/emacs -Q -l .../elpa/packages/nhexl-mode/nhexl-mode.el README
> M-x nhexl-mode RET
> <page-down>
> 
> You'll see at the top of the screen that the window-start is in the
> middle of one of the (display) lines, even though none of the display
> lines are particularly long.

Similar problems happen in Emacs 23.3, although there they are only
visible if you move cursor vertically with C-n until Emacs scrolls the
display.  So this is not a regression wrt Emacs 23.

I will look into this in a couple of days.