Fix fast-logger 2.0.1 for GHC 7.4

patching/patches/fast-logger-2.0.1.patch

@@ -0,0 +1,19 @@
+diff -ru orig/System/Log/FastLogger/Logger.hs new/System/Log/FastLogger/Logger.hs
+--- orig/System/Log/FastLogger/Logger.hs	2013-12-24 08:14:25.325658733 +0200
++++ new/System/Log/FastLogger/Logger.hs	2013-12-24 08:14:24.000000000 +0200
+@@ -19,6 +19,15 @@
+ 
+ data Logger = Logger (MVar Buffer) !BufSize (IORef LogStr)
+ 
++#if !MIN_VERSION_base(4, 6, 0)
++atomicModifyIORef' :: IORef a -> (a -> (a,b)) -> IO b
++atomicModifyIORef' ref f = do
++    b <- atomicModifyIORef ref
++            (\x -> let (a, b) = f x
++                    in (a, a `seq` b))
++    b `seq` return b
++#endif
++
+ newLogger :: BufSize -> IO Logger
+ newLogger size = do
+     buf <- getBuffer size