(maint) Windows file provider :links => :follow

- Previously, the Windows file provider would raise an error when
   applying a catalog that contained file resources with `:links =>
   :follow`, when the given path was not actually a symlink
 - The behavior of readlink is essentially correct, as File.readlink on
   other operating systems yields Errno::EINVAL: Invalid argument
 - Therefore the appropriate behavior to match Puppet on other
   platforms is to behave like File.chown, which will operate on the
   link IFF it is one, or will operate on the file / dir directly if it
   is not a link
 - Corrected a minor issue in the creation of the error msg raised
   by the Windows implementation of readlink