Given the high impact of this change, we decided to back off and make
abstract newtypes give a warning for one release, before we make it an
error in 7.6.1.

Codec/Compression/Zlib/Stream.hsc:884:1:
    Warning: newtype `CInt' is used in an FFI declaration,
             but its constructor is not in scope.
             This will become an error in GHC 7.6.1.
    When checking declaration:
      foreign import ccall unsafe "static zlib.h deflate" c_deflate
        :: StreamState -> CInt -> IO CInt