Merge remote-tracking branch 'upstream/8.x' into kernel

core/includes/form.inc

core/lib/Drupal/Core/StreamWrapper/LocalStream.php

...b/Drupal/Core/StreamWrapper/PhpStreamWrapperInterface.php

core/lib/Drupal/Core/StreamWrapper/PrivateStream.php

core/lib/Drupal/Core/StreamWrapper/PublicStream.php

.../lib/Drupal/Core/StreamWrapper/StreamWrapperInterface.php

core/lib/Drupal/Core/StreamWrapper/TemporaryStream.php

core/modules/field/modules/options/options.module

core/modules/field/tests/field.test

core/modules/locale/locale.module

core/modules/rdf/rdf.module

core/modules/simpletest/tests/form.test

core/modules/simpletest/tests/form_test.module