php5.3.* compatibility

line 58:
$zipFolder = $tmpDir . '/' . rtrim($zip->statIndex(0)['name'], "/");

replaced by :
$zipFolders = $zip->statIndex(0);
$zipFolder = $tmpDir . '/' . rtrim($zipFolders['name'], "/");

making "zf.php install zf anydir" working with php5.3.*