Fix the error message parser and add TwitterUnknownErrorResponse to T…

…witterError.

The Twitter documentation says that the error response looks like this:

  {"errors":[{"message":"Sorry, that page does not exist","code":34}]}

However, Twitter occasionally responds error responses, formatted as an undocumented form, such as:

  {"errors":"...."}

Web/Twitter/Conduit/Base.hs

@@ -116,10 +116,12 @@ checkResponse :: Response Value
               -> Either TwitterError Value
 checkResponse Response{..} =
     case responseBody ^? key "errors" of
-        Just errs ->
+        Just errs@(Array _) ->
             case fromJSON errs of
                 Success errList -> Left $ TwitterErrorResponse responseStatus responseHeaders errList
                 Error msg -> Left $ FromJSONError msg
+        Just err ->
+            Left $ TwitterUnknownErrorResponse responseStatus responseHeaders err
         Nothing ->
             if sci < 200 || sci > 400
                 then Left $ TwitterStatusError responseStatus responseHeaders responseBody

Web/Twitter/Conduit/Response.hs

@@ -28,6 +28,7 @@ data Response responseType = Response
 data TwitterError
     = FromJSONError String
     | TwitterErrorResponse Status ResponseHeaders [TwitterErrorMessage]
+    | TwitterUnknownErrorResponse Status ResponseHeaders Value
     | TwitterStatusError Status ResponseHeaders Value
     deriving (Show, Typeable, Eq)