6863864: (fs) Path.createSymbolicLink doesn't set directory flag when creating sym link to directory (win)

[Alan Bateman]

Sherman - do you mind reviewing this one?

It's a small over sight in the implementation of Path#createSymbolicLink 
on Windows. Sym links to files and different to sym links to directories 
so there is a check on the target type that is incorrect for the case 
that the target is a relative path without a root component (other cases 
are okay). There is also a corner case when creating a sym link to a 
existing directory sym link where the final target doesn't exist. I've 
fixed both of these issues and improved the test coverage. The webrev is 
here:
    http://cr.openjdk.java.net/~alanb/6863864/webrev.00/

Thanks,
Alan.