basic json support

This includes a generic JSONStream library built on top of Text.JSON
(somewhat hackishly).

It would be possible to stream out a single json document describing
all actions, but it's probably better for consumers if they can expect
one json document per line, so I did it that way instead.

Output from external programs used for transferring files is not
currently hidden when outputting json, which probably makes it not very
useful there. This may be dealt with if there is demand for json
output for --get or --move to be parsable.

The version, status, and find subcommands have hand-crafted output and
don't do json. The whereis subcommand needs to be modified to produce
useful json.

Utility/JSONStream.hs

@@ -0,0 +1,44 @@
+{- Streaming JSON output.
+ -
+ - Copyright 2011 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Utility.JSONStream (
+	start,
+	add,
+	end
+) where
+
+import Text.JSON
+
+{- Text.JSON does not support building up a larger JSON document piece by
+   piece as a stream. To support streaming, a hack. The JSObject is converted
+   to a string with its final "}" is left off, allowing it to be added to
+   later. -}
+start :: JSON a => [(String, a)] -> String
+start l
+	| last s == endchar = take (length s - 1)  s
+	| otherwise = bad s
+	where
+		s = encodeStrict $ toJSObject l
+
+add :: JSON a => [(String, a)] -> String
+add l
+	| head s == startchar = ',' : drop 1 s
+	| otherwise = bad s
+	where
+		s = start l
+
+end :: String
+end = [endchar, '\n']
+
+startchar :: Char
+startchar = '{'
+
+endchar :: Char
+endchar = '}'
+
+bad :: String -> a
+bad s = error $ "Text.JSON returned unexpected string: " ++ s