* (bug 2587) Fix for section editing with comment prefix

* (bug 2587) Fix for section editing with comment prefix
* (bug 2607) Fix for section editing with mix of wiki and HTML headings
* (bug 3342) Fix for section editing with headings wrapped in <noinclude>
* (bug 3476) Fix for section editing with faux headings in extensions
* (bug 5272) Fix for section editing with HTML-heading subsections
* Fix for bogus wiki headings improperly detected with following text
* Fix for HTML headings improperly not detected with preceding/following text
* Section extraction and replacement functions merged into one implementation
  on the Parser object, so they can't get out of sync with each other.