Add missing test for db4 handler

ext/dba/tests/dba_db4.phpt

@@ -0,0 +1,29 @@
+--TEST--
+DBA DB4 handler test
+--SKIPIF--
+<?php 
+	require_once('skipif.inc');
+	if (!in_array('db4', dba_handlers())) die('skip DB4 handler not available');
+?>
+--FILE--
+<?php
+	require_once('test.inc');
+	$handler = ini_get('dba.default_handler');//'db4';
+	require_once('dba_handler.inc');
+?>
+--EXPECT--
+database handler: db4
+3NYNYY
+Content String 2
+Content 2 replaced
+Read during write: not allowed
+Content 2 replaced 2nd time
+The 6th value
+array(3) {
+  ["key number 6"]=>
+  string(13) "The 6th value"
+  ["key2"]=>
+  string(27) "Content 2 replaced 2nd time"
+  ["key5"]=>
+  string(23) "The last content string"
+}