PHP date format strings are not extracted from config

There was some suspicion that not all core configuration strings are found with the potx parser. Eg. some views portions, etc. To verify that I did the following:

1. Installed Drupal 8 RC3 locally.
2. Installed all the core modules.
3. Added a foreign language.
4 Run this query on the DB (output attached):

SELECT name, sid, source, context FROM `locales_location` left join locales_source on locales_location.sid = locales_source.lid where type = "configuration"

5. Downloaded Ukrainian translation (the .pot export of RC3 is timing out on localize and the Ukrainian team is 100%, so they were a good test).
6. Ran this simple script on them:

$translation = file_get_contents('drupal-8.0.0-rc3.uk.po');
if (($handle = fopen("locales_location.csv", "r")) !== FALSE) {
    while (($data = fgetcsv($handle, 1000, ";")) !== FALSE) {
      if (!strpos($translation, $data[2])) {
      	print $data[2] . ' --- ' . $data[3] . "\n";
      }
    }
    fclose($handle);
}

This found several false positives. I did not want to futz with trying to do the same string breakup as in the .po file. So manually checked a few of each type of string (tour, email, etc). All seem to be in the localize copy EXCEPT:

l, F j, Y - H:i --- PHP date format
D, m/d/Y - H:i --- PHP date format
m/d/Y - H:i --- PHP date format

So apparently we have some problem with translating the default date formats.