Helper function to sort requirements.
function _system_sort_requirements($a, $b) {
if (!isset($a['weight'])) {
if (!isset($b['weight'])) {
return strcasecmp($a['title'], $b['title']);
}
return -$b['weight'];
}
return isset($b['weight']) ? $a['weight'] - $b['weight'] : $a['weight'];
}