patch 8.0.1278: GUI window always resizes when adding scrollbar

Problem:    GUI window always resizes when adding/removing a scrollbar,
            toolbar, etc.
Solution:   Add the 'k' flag in 'guioptions' to keep the GUI window size and
            change the number of lines/columns instead. (Ychin, closes #703)
diff --git a/src/gui_gtk_x11.c b/src/gui_gtk_x11.c
index 9be54b9..83b98e1 100644
--- a/src/gui_gtk_x11.c
+++ b/src/gui_gtk_x11.c
@@ -2938,7 +2938,7 @@
     if (gui.norm_font != NULL)
     {
 	gui_mch_init_font(p_guifont, FALSE);
-	gui_set_shellsize(FALSE, FALSE, RESIZE_BOTH);
+	gui_set_shellsize(TRUE, FALSE, RESIZE_BOTH);
     }
 }
 
@@ -4909,8 +4909,9 @@
 }
 
 /*
- * Called when the font changed while the window is maximized.  Compute the
- * new Rows and Columns.  This is like resizing the window.
+ * Called when the font changed while the window is maximized or GO_KEEPWINSIZE
+ * is set.  Compute the new Rows and Columns.  This is like resizing the
+ * window.
  */
     void
 gui_mch_newfont(void)