bug#7839: 24.0.50; Truncated lines: clicking right fringe arrows is broken

[Stephen Berman <stephen.berman@gmx.net>]

1. emacs -Q
2. Type C-x 3 to split the window horizontally, so that the text in
*scratch* is truncated.
3. Click on one of the arrows in the right finge.
=> The cursor jumps to the beginning of the line, instead of the display
being moved to the right, as it used to and as is documented in
(emacs)Fringes.  

Note that it is only clicking the arrow in the right fringe that fails:
clicking in the text area within hscroll-margin of the fringe does move
the display, and when there are arrows in the left margin, clicking
these moves the display to the left.

I don't know when this bug appeared, but I think it was within the past
month or so, maybe longer ago.

In GNU Emacs 24.0.50.1 (i686-pc-linux-gnu, GTK+ Version 2.20.1)
 of 2011-01-13 on escher
Windowing system distributor `The X.Org Foundation', version 11.0.10800000
configured using `configure  '--without-toolkit-scroll-bars' 'CFLAGS=-g -O2 -fno-optimize-sibling-calls''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=local
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t