------------------
- fixed content-type with charset
[tom_gross, thanks Steve Spicklemire]
- changed `has_key` with __contains__ calls
[tom_gross]
- fixed sending of unauthorized status
[tom_gross]
- return error object according to the JSON-RPC specification
http://json-rpc.org/wd/JSON-RPC-1-1-WD-20060807.htmlErrorObject
[tom_gross, thanks Steve Spicklemire]