JSON-RPC status

The JSON-RPC implementation is going well.  I'm using boost::asio for
sockets.  JSON-RPC can be plain socket or HTTP, but it seems most other
implementations are HTTP, so I made my own simple HTTP headers.  For
JSON parsing I'm using JSON Spirit, which makes full use of STL and has
been really nice to use.  It's header-only so it's no added build work,
and small enough to just add it to our source tree.  MIT license.  This
should all be working in a few more days.

The forum sure is taking off.  I didn't expect to have so much activity
so fast.