Added ping time measurement.
New RPC "ping" command to request ping.
Implemented "pong" message handler.
New "pingtime" field in getpeerinfo, to provide results to user.
New "pingwait" field, to show pings still in flight, to better see newly lagging peers.
Merge pull request #2937

971bb3e Added ping time measurement. New RPC "ping" command to request ping. Implemented "pong" message handler. New "pingtime" field in getpeerinfo, to provide results to user. New "pingwait" field, to show pings still in flight, to better see newly lagging peers. (Josh Lehan)