AutoP filter should handle intentionally added line breaks

When autop filter is turned on, the preg_replace function shown above, makes paragraphs on paragraphs that end with double space.

      // make paragraphs, including one at the end
      $chunk = '<p>' . preg_replace('/\n\s*\n\n?(.)/', "</p>\n<p>$1", $chunk) . "</p>\n";

So, when the filter would work on is:

  $input = "aaa\nbbb\n\nccc\n\n\nddd\n\n\n\neee";
  $output = FilterAutoP::process($input);     // output:  "<p>aaa<br />\nbbb</p>\n<p>ccc</p>\n<p>ddd</p>\n<p>eee</p>"

The extra line breaks created should be processed as additional linebreaks:

  $input = "aaa\nbbb\n\nccc\n\n\nddd\n\n\n\neee";
  $output = FilterAutoP::process($input);     // output:  "<p>aaa<br />\nbbb</p>\n<p>ccc<br />\n</p>\n<p>ddd<br />\n<br />\n</p>\n<p>eee</p>"