Separated find queries for request 'h1,h2,h3'

In original jQuery, `$('h1,h2,h3')` returns a collection of elements sorted by their location in document.
In phpQuery, `['h1,h2,h3']` launch separated find queries for h1, h2 and h3. So the result collection is sorted by tag name in the find request.
In this case it is unable to quickly build a document's table of contents (headers hierarchy).
