bug#3396: next-line and previous-line do not work correctly near long lines

[Shannon Jones]

This is similar to bug#3386 posted by Heinrich Rommerskirchen.  It's somewhat 
different, so I decided to post a new bug report.

* Emacs version: GNU Emacs 23.0.94.1 (i686-pc-linux-gnu, GTK+ Version 2.10.4) 
of 2009-05-26

Also reproduced on 23.0.94.1 on Windows.

* Compiled on CentOS 5.3.

* No options given to configure

* To reproduce:

Run: emacs -Q (happens with or without -nw)
C-x b *scratch*
C-u 1000 X
<RET>

This will put 1000 X's on the screen and the cursor will be on the line below 
them.  The line of X's should wrap over several lines of the screen with 
continuation marks at the end of each line.

Hit C-p. This *should* put the cursor at the beginning of the line of X's.  
Instead, it puts the cursor at the left column on the screen, but somewhere in 
the middle of the line of X's.  Hitting C-p again a few times moves the cursor 
somewhere else on the line, but still at the left-most column. Hitting C-n now 
should move you to the beginning of the next physical line (the blank one after 
the X's), but instead moves you somewhere else on the line of X's (but still in 
the first column).

In other words, next-line and previous-line should move relative to physical 
lines in the file, but are instead moving relative to lines on the screen.  
Changing the screen width changes the behavior of C-n and C-p when the lines 
are long enough to wrap.

This is different from Emacs 22.  I noticed this when writing macros that do 
something to one line, then move to the next line at the end macro to prepare 
for the next run.  The macro failed on lines that were longer than my screen 
width.