touch files with high-resolution timestamp

Needs unix 2.7.2, but that was included in ghc 8.0.1 (and much older)
so not really a new dep.

Command/Fix.hs

@@ -93,7 +93,7 @@ fixSymlink file link = do
 	liftIO $ do
 #if ! defined(mingw32_HOST_OS)
 		-- preserve mtime of symlink
-		mtime <- catchMaybeIO $ TimeSpec . modificationTime
+		mtime <- catchMaybeIO $ modificationTimeHighRes
 			<$> getSymbolicLinkStatus file
 #endif
 		createDirectoryIfMissing True (parentDir file)