204/304 responses should not have content-length

Should fix #242 for 0.9.

Author: gregorycollins

snap-core.cabal

@@ -1,5 +1,5 @@
 name:           snap-core
-version:        0.9.7.2
+version:        0.9.8.0
 synopsis:       Snap: A Haskell Web Framework (core interfaces and types)
 
 description:

src/Snap/Internal/Types.hs

@@ -978,7 +978,7 @@ fixupResponse req rsp = {-# SCC "fixupResponse" #-} do
     handle304 :: Response -> Response
     handle304 r = setResponseBody (enumBuilder mempty) $
                   updateHeaders (H.delete "Transfer-Encoding") $
-                  setContentLength 0 r
+                  clearContentLength r
 {-# INLINE fixupResponse #-}