still can't express custom-setup deps

They need unix on non-windows, for Utility.Env, which Build.Configure uses,
but cabal can't express that in a custom-setup stanza.

To avoid this problem, Utility.Env would need to be moved into
unix-compat..

Build/Configure.hs

@@ -7,7 +7,6 @@ module Build.Configure where
 import Control.Applicative
 import Control.Monad.IfElse
 import Control.Monad
-import System.Directory
 
 import Build.TestConfig
 import Build.Version
@@ -19,6 +18,7 @@ import Utility.Env
 import Utility.Exception
 import qualified Git.Version
 import Utility.DottedVersion
+import Utility.Directory
 
 tests :: [TestCase]
 tests =