gtk_selection_clear_targets() does not exist on GTK 1, so ifdef it.

[originally from svn r8371]

unix/gtkwin.c

@@ -1640,7 +1640,9 @@ void write_clip(void *frontend, wchar_t * data, int *attr, int len, int must_des
 
     if (gtk_selection_owner_set(inst->area, GDK_SELECTION_PRIMARY,
 				inst->input_event_time)) {
+#if GTK_CHECK_VERSION(2,0,0)
 	gtk_selection_clear_targets(inst->area, GDK_SELECTION_PRIMARY);
+#endif
 	gtk_selection_add_target(inst->area, GDK_SELECTION_PRIMARY,
 				 GDK_SELECTION_TYPE_STRING, 1);
 	if (inst->pasteout_data_ctext)