PHP 5.5.13 and 5.5.15 are *sometimes* failing

The DOMDocument::saveHTML function is occassionally (about 75% of the time) failing to return any content.

Also, we need to leave `$content` untouched in case we need to return it.

AND! we are updating the theme to directly call the function and avoid a filter (https://github.com/GigaOM/gigaom/pull/5718)