Preserve unnormalized path when enumerating DFS Links.

Enumerated DFS links tend to have normalized server names
in the path, either all uppercase, or FQDN, or both.
This change re-resolves the link against our supplied Namespace
in WindowsFileDelegate.enumerateDfsLinks.

This change also eliminates a log message thrown when we fail to
retrieve DFS information for a path. Now that isDfsLink() is called
for every file and folder crawled, this just filled the logs with
useless log statements.  In the case where getting the DFS info
really matters, the adaptor throws IOException anyway.

Code Review:  http://codereview.appspot.com/189240043