Fix b/1753517: Hidden Folders should not be crawled.

This fixes a bug in NioFileDelegate.isHidden().
It seems that NIO Files.isHidden(Path) does not consider hidden
folders to be hidden.  From the NIO Files javadoc:
"On Windows a file is considered hidden if it isn't a directory
 and the DOS hidden attribute is set."

I don't know why Sun/Oracle decided to exclude hidden directories.
Consequently, I changed the implementation to use File.isHidden(),
which does pay attention to the hidden attribute on directories.

Code Review: http://codereview.appspot.com/85580045
1 file changed