Description:
------------
When I call the tempnam() function, it always returns a file located in the system temp directory (C:\WINNT\TEMP) even if I specify an existing directory.

Reproduce code:
---------------
class TxtFile
{
  var $_tmp_dir = '/web/tmp/';

  function gentmp() {
    $tmp = '';
    if( is_dir( $this->_tmp_dir ) )
      $tmp = tempnam( $this->_tmp_dir, get_class($this) );
      // $tmp is always located in 'C:\WINNT\TEMP\' even
      // if specified directory exists...
    return $tmp;
  }
}

$txt = new TxtFile();
echo $txt->gentmp();

Expected result:
----------------
/web/tmp/txt9375.tmp

Actual result:
--------------
C:\WINNT\TEMP\txt9375.tmp