bug#1810: 23.0.60; visual-line-mode moves to the wrong column

[Juri Linkov <juri@jurta.org>]

When `line-move-visual' is non-nil, moving down from a control character
moves to the wrong column.

Test case:

1. insert to a new buffer the following text:

^@est.
Test2.
Test3.

where ^@ at the beginning of the buffer is a NULL control character.

2. Move to the beginning of the buffer (M-<).

3. Move down (C-n) - point jumps from the *first* column of the first line
to the *second* column of the second line.

This behavior can be traced back to the function `posn-at-point'
that returns the x-coordinate of the second character in the displayed
control sequence "^@" instead of the first character where point
is actually located.

-- 
Juri Linkov
http://www.jurta.org/emacs/