Fix tab stops when line numbers are displayed

* src/xdisp.c (x_produce_glyphs):
* src/term.c (produce_glyphs): Adjust tab stops for the horizontal
space taken by the line-number display.

src/term.c

@@ -1584,6 +1584,10 @@ produce_glyphs (struct it *it)
     {
       int absolute_x = (it->current_x
 			+ it->continuation_lines_width);
+      /* Adjust for line numbers.  Kludge alert: the "2" below is
+	 because we add 2 blanks to the actual line number.  */
+      if (!NILP (Vdisplay_line_numbers))
+	absolute_x -= it->lnum_width + 2;
       int next_tab_x
 	= (((1 + absolute_x + it->tab_width - 1)
 	    / it->tab_width)

src/xdisp.c

@@ -27865,6 +27865,10 @@ x_produce_glyphs (struct it *it)
 	    {
 	      int tab_width = it->tab_width * font->space_width;
 	      int x = it->current_x + it->continuation_lines_width;
+	      /* Adjust for line numbers.  Kludge alert: the "2" below
+		 is because we add 2 blanks to the actual line number.  */
+	      if (!NILP (Vdisplay_line_numbers))
+		x -= (it->lnum_width + 2) * font->space_width;
 	      int next_tab_x = ((1 + x + tab_width - 1) / tab_width) * tab_width;
 
 	      /* If the distance from the current position to the next tab