fileinput-directory test

Hello,
We are using Modernizr in production on www.centraldesktop.com - thank you for all the work involved in creating it! 
Recently we found that we need to detect ability to select folders in <input type="file"> by reading `webkitdirectory` or `directory` attribute on file input. Because this test is missing in Modernizr, we have created it and would like to contribute it to community tests.
Thank you for your consideration.
Alexander