[introspection] mark invokers for gtkeditable vfuncs

gtk/gtkeditable.c

@@ -199,6 +199,8 @@ gtk_editable_base_init (gpointer g_class)
  *
  * Note that the position is in characters, not in bytes. 
  * The function updates @position to point after the newly inserted text.
+ *
+ * Virtual: do_insert_text
  */
 void
 gtk_editable_insert_text (GtkEditable *editable,
@@ -373,6 +375,8 @@ gtk_editable_delete_selection (GtkEditable *editable)
  * the end of the text.
  * 
  * Note that positions are specified in characters, not bytes.
+ *
+ * Virtual: set_selection_bounds
  */
 void
 gtk_editable_select_region (GtkEditable *editable,