Y.Selector returns incorrect # of elements when queried against doc frags

(This is to "reissue" the closed request discussed here: https://github.com/yui/yui3/pull/879)
  
On browsers who don't support support `getElementsByTagName` or `querySelectorAll` on document fragments, we are forced to traverse the fragment manually to get all of the elements it contains. When `querySelectorAll` isn't present, `Y.Selector` will return an incorrect # of elements.

Here's a jsfiddle demonstrating this error: http://jsfiddle.net/2k9Rh/1/

I added:
* Correction of the previously flawed `getElementsByTagName` algorithm.
* Unit tests to ensure the correct elements are being returned.