Proper GHC conditionals to fix compiler warnings

hpath.cabal

@@ -19,7 +19,10 @@ extra-source-files:  README.md
 library
   hs-source-dirs:    src/
   default-language:  Haskell2010
-  ghc-options:       -Wall
+  if impl(ghc >= 8.0)
+    ghc-options:       -Wall -Wno-redundant-constraints
+  else
+    ghc-options:       -Wall
   c-sources:         cbits/dirutils.c
   exposed-modules:   HPath,
                      HPath.IO,

src/System/Posix/Directory/Traversals.hs

@@ -10,6 +10,7 @@
 -- Traversal and read operations on directories.
 
 
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE ForeignFunctionInterface #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE PackageImports #-}
@@ -37,7 +38,10 @@ module System.Posix.Directory.Traversals (
 , realpath
 ) where
 
-import Control.Applicative
+
+#if __GLASGOW_HASKELL__ < 710
+import Control.Applicative ((<$>))
+#endif
 import Control.Monad
 import System.Posix.FilePath ((</>))
 import System.Posix.Directory.Foreign