private function _mergeDependencyVersions(array $array1, array $array2) {
        foreach ($array2 as $package => $version) {
            if (!isset($array1[$package])) {
                $array1[$package] = $version;
            } else {
                if ($array1[$package] != $version) {
                    $array1[$package] .= " ".$version;
                }
            }
        }
        return $array1;
    }