if (!function_exists('file_put_contents')) {
function file_put_contents($filename, $data) {
$f = @fopen($filename, 'w');
if (!$f) {
return false;
} else {
$bytes = fwrite($f, $data);
fclose($f);
return $bytes;
}
}
}

Just to make sure that you keep compatibility in case you get some updates/add-ons whatever that could insert a file_put_contents somewhere in the code. The same goes for any other PHP5 only function (most can be replicated in PHP4 as well)