Date granularity is too fragile in date_field_all_day()

In date.module, date_field_all_day() does following:

$granularity = $field['settings']['granularity'];
$granularity = array_pop($granularity);

When the granularity is properly ordered greatest to smallest, this works fine.
However, when exporting a field using Features, all associated arrays of settings are ksort()-ed, so (year, month, day, hour, minute, second) becomes (day, hour, minute, month, second, year), and the granularity is returned as year instead of second.

In debugging this, I came across the date_granularity_sorted() and date_granularity_precision() functions. The latter didn't work, as it called clone() on an array. But some tweaking, and the issue is fixed, and the code is much clearer.