drop incremental json object display; clean up code

This gets rid of quite a lot of ugly hacks around json generation.

I doubt that any real-world json parsers can parse incomplete objects, so
while it's not as nice to need to wait for the complete object, especially
for commands like `git annex info` that take a while, it doesn't seem worth
the added complexity.

This also causes the order of fields within the json objects to be
reordered. Since any real json parser shouldn't care, the only possible
problem would be with ad-hoc parsers of the old json output.

Types/Messages.hs

@@ -10,7 +10,7 @@
 module Types.Messages where
 
 import Data.Default
-import qualified Data.ByteString.Lazy as B
+import qualified Data.Aeson as Aeson
 
 #ifdef WITH_CONCURRENTOUTPUT
 import System.Console.Regions (ConsoleRegion)
@@ -31,7 +31,7 @@ data MessageState = MessageState
 	, consoleRegion :: Maybe ConsoleRegion
 	, consoleRegionErrFlag :: Bool
 #endif
-	, jsonBuffer :: B.ByteString
+	, jsonBuffer :: Maybe Aeson.Object
 	}
 
 instance Default MessageState
@@ -45,5 +45,5 @@ instance Default MessageState
 		, consoleRegion = Nothing
 		, consoleRegionErrFlag = False
 #endif
-		, jsonBuffer = B.empty
+		, jsonBuffer = Nothing
 		}