Deprecate GtkComboBoxEntry in favor of added properties to GtkComboBox

GtkComboBox now sports a construct-only "has-entry" property which
decides if it uses a GtkEntry to allow additional user input. Also
it has a new "entry-text-column" to fetch strings for the entry
from the model.

This patch deprecates the GtkComboBoxEntry and updates the rest of GTK+
to use the new semantics on GtkComboBox instead.

GtkComboBoxEntry will be removed altogether before GTK+ 3, in a
later commit.

demos/gtk-demo/combobox.c

@@ -428,7 +428,14 @@ do_combobox (GtkWidget *do_widget)
     gtk_container_set_border_width (GTK_CONTAINER (box), 5);
     gtk_container_add (GTK_CONTAINER (frame), box);
     
-    combo = gtk_combo_box_entry_new_text ();
+    model = (GtkTreeModel *)gtk_list_store_new (1, G_TYPE_STRING);
+    combo = g_object_new (GTK_TYPE_COMBO_BOX,
+                          "has-entry", TRUE,
+                          "model", model,
+                          "entry-text-column", 0,
+                          NULL);
+    g_object_unref (model);
+
     fill_combo_entry (combo);
     gtk_container_add (GTK_CONTAINER (box), combo);