Avoid leaving traces of cursor when entering linum-mode.

 src/fringe.c (draw_fringe_bitmap_1): Don't reduce the width of the
 left fringe if the window has a left margin.  This avoids leaving
 traces of the cursor because its leftmost pixel is not drawn over.

src/ChangeLog

 2012-09-09  Eli Zaretskii  <eliz@gnu.org>
+	* fringe.c (draw_fringe_bitmap_1): Don't reduce the width of the
+	left fringe if the window has a left margin.  This avoids leaving
+	traces of the cursor because its leftmost pixel is not drawn over.
+
 	* dispnew.c (update_window_line): When the left margin area of a
 	screen line is updated, set the redraw_fringe_bitmaps_p flag of
 	that screen line.  (Bug#12277)

src/fringe.c

@@ -659,7 +659,14 @@ draw_fringe_bitmap_1 (struct window *w, struct glyph_row *row, int left_p, int o
 	{
 	  /* If W has a vertical border to its left, don't draw over it.  */
 	  wd -= ((!WINDOW_LEFTMOST_P (w)
-		  && !WINDOW_HAS_VERTICAL_SCROLL_BAR (w))
+		  && !WINDOW_HAS_VERTICAL_SCROLL_BAR (w)
+		  /* But don't reduce the fringe width if the window
+		     has a left margin, because that means we are not
+		     in danger of drawing over the vertical border,
+		     and OTOH leaving out that one pixel leaves behind
+		     traces of the cursor, if it was in column zero
+		     before drawing non-empty margin area.  */
+		  && NILP (w->left_margin_cols))
 		 ? 1 : 0);
 	  p.bx = x - wd;
 	  p.nx = wd;