Fixes as a result of profiling the HTTP code and control channel

There are the following issues pertaining to JSONFeed and Http parsers which per my profiling tests seems to be first candidates for fixing:

• JSONFeed::postBuffer expensive because of making new allocations all the time
• JSONFeed::popNextFromBuffer makes many buffer de-allocations
• JSONFeed::innerJSONHandler should not transition if the state remains the same
• HttpResponseParser body handler is inefficient as it reads characters one by one
• Connection::doTransaction should not reinitialize the parser all the time as it triggers expensive reinitialization of the state machine