fix for sigsegv in case of drag_target == NULL fix for

fix for sigsegv in case of drag_target == NULL fix for

* gtk/gtkctree.c (gtk_ctree_button_release): fix for sigsegv in
  case of drag_target == NULL
* gtk/gtkclist.c (gtk_clist_button_press): fix for GTK_2/3BUTTON_PRESS.
  Clist did not emit an select_row signal in case of GTK_2/3BUTTON_PRESS.
* gtk/gtkfilesel.c (gtk_file_selection_file_button,
  gtk_dir_selection_file_button): fix due to changes in clist's
  select_row signal.