Update all the list box code in gtkdlg.c to use the new-style GTK2

GtkTreeView, GtkComboBox and GtkComboBoxEntry instead of the various
old deprecated stuff. Immediate benefit: GTK2 natively supports real
drag lists, hooray!

[originally from svn r7959]

dialog.h

@@ -209,6 +209,10 @@ union control {
 	 * has a drop-down list built in. (Note that a _non_-
 	 * editable drop-down list is done as a special case of a
 	 * list box.)
+	 * 
+	 * Don't try setting has_list and password on the same
+	 * control; front ends are not required to support that
+	 * combination.
 	 */
 	int has_list;
 	/*
@@ -333,6 +337,11 @@ union control {
 	 * the respective widths of `ncols' columns, which together
 	 * will exactly fit the width of the list box. Otherwise
 	 * `percentages' must be NULL.
+	 * 
+	 * There should never be more than one column in a
+	 * drop-down list (one with height==0), because front ends
+	 * may have to implement it as a special case of an
+	 * editable combo box.
 	 */
 	int ncols;		       /* number of columns */
 	int *percentages;	       /* % width of each column */

unix/GTK2.TODO

@@ -16,9 +16,6 @@ Things to do before deciding a merge is feasible:
    large chunks we should have reimplemented and haven't, or indeed
    that we shouldn't have reimplemented and have.
 
- - Uses of GtkList should be replaced with the non-deprecated
-   GtkTreeView.
-
  - Investigate the shortcut mechanism in GTK2's GtkLabel, and see if
    it's worth switching to it from the current ad-hockery.
 
@@ -35,6 +32,9 @@ Things to do before deciding a merge is feasible:
 Things to do once GTK2 development is complete:
 
  - Make sure we haven't broken GTK1.
+    + In particular, I know I _have_ broken GTK1 by taking out all
+      the GTK1-style list box code. Put it all back in under ifdefs,
+      which will be unpleasant but necessary.
 
 Things to do at point of actual merge: