Squashed 'src/leveldb/' changes from be1b0ff..936b461

936b461 Merge upstream LevelDB 1.13.
748539c LevelDB 1.13

git-subtree-dir: src/leveldb
git-subtree-split: 936b4613ea4551992e6096b1e05eeefc09a20e3b
Merge src/leveldb changes for LevelDB 1.13
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.
Refactor/encapsulate chain globals into a CChain class
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)
[doc] Add testnet hidden service port to the example tor config.

Seems like there are a lot of advertised testnet HS nodes that
don't actually work. Lack of the testnet port on the example
HS config might be one reason.
Merge pull request #3089 from gmaxwell/hsport

[doc] Add testnet hidden service port to the example tor config.
Merge pull request #2933 from sipa/leveldb113

Merge upstream LevelDB 1.13
Merge pull request #3077 from sipa/chain

Refactor/encapsulate chain globals into a CChain class
Avoid core dump if rpc port is in use.

The cleanup code needs to check for NULL rpcworkers thread group.