Context doesn't render regions in the same order as Core

When context renders blocks, it does so by region. When it loops through the regions and renders associated blocks, it does so in no particular order, which defaults to whichever region happened to be listed first in the declaration of block reactions.

For instance, in the following example, the content region would be rendered first, followed by the header_top region.

$context->reactions = array(
  'block' => array(
    'blocks' => array(
      'system-main' => array(
        'module' => 'system',
        'delta' => 'main',
        'region' => 'content',
        'weight' => 0,
      ),
      'delta_blocks-logo' => array(
        'module' => 'delta_blocks',
        'delta' => 'logo',
        'region' => 'header_top',
        'weight' => -10,
      ),
    ),
  ),
);

While the following would render the header_top region first, followed by the content region.

$context->reactions = array(
  'block' => array(
    'blocks' => array(
      'delta_blocks-logo' => array(
        'module' => 'delta_blocks',
        'delta' => 'logo',
        'region' => 'header_top',
        'weight' => -10,
      ),
      'system-main' => array(
        'module' => 'system',
        'delta' => 'main',
        'region' => 'content',
        'weight' => 0,
      ),
    ),
  ),
);

This is especially a problem if you use the Delta module (to place Drupal messages in certain regions) and the Formblock module (to place, e.g. a User Registration form in different regions). In some combinations, the form will be processed after the messages are rendered, resulting in no error messages being displayed until the next page load.

The solution would involve sorting the regions before rendering the region's blocks in context_reaction_block::block_list() in a way that matched system_region_list().