Fix build with directory-1.2.6.2.

It started exporting a isSymbolicLink which supports windows. But,
git-annex does no use symlinks on windows yet and this conflicts with the
function by the same name from unix-compat, so hide it.

Build/Version.hs

@@ -6,7 +6,7 @@ module Build.Version where
 
 import Data.List
 import System.Environment
-import System.Directory
+import System.Directory hiding (isSymbolicLink)
 import Data.Char
 import System.Process
 import Control.Applicative