Correct Nav.php comments/PHP doc to reflect BS3 dropdown support.

Corrected the example and doc to highlight allowed dropdown support in Bootstrap 3.
Correct Nav.php comments/PHP doc to reflect BS3 dropdown support.

Updated tabs
Correct Nav.php comments/PHP doc to reflect BS3 dropdown support.

Removed edited author ref.
Merge pull request #1291 from kartik-v/patch-3

Correct Nav.php comments/PHP doc to reflect BS3 dropdown support.