Improve transaction security
* Check signatures of every transaction on every validator
* Remove obsolete code
* Check transaction status in submit/sign RPC handler
Set version to 0.26.3-sp2
Use trusted validators median fee
Set version to 0.26.3-sp4
Attempt to fix spurious travis failures
Guarantee C locale

*  Remove all calls to setlocale to ensure that the global
   locale is always C.

*  Also replace beast::SystemStats::getNumCpus() with
   std::thread::hardware_concurrency()
Gracefully cast from std::thread::hardware_concurrency
Silence clang warnings
Remove Og from debug mode

Last time I used gdb, iterating over a directory's `Indexes`, each uint256 printed as `<optimized out>`.

Debug mode is for debugging ...
SHAMap performance improvements (RIPD-434)

This reworks the way SHAMaps are stored, flushed, backed, and
traversed. Rather than storing the linkages in the SHAMap itself,
that information is now stored in the nodes. This makes
snapshotting much cheaper and also allows traverse work done on
behalf of one SHAMap to be used by other SHAMaps that share inner
nodes with that SHAMap.

When a SHAMap is modified, nodes are modified all the way up to the
root. This means that the modified nodes in a SHAMap can easily be
traversed for flushing. So they don't need to be separately tracked.

Summary
* Remove mTNByID
* Remove mDirtyNodes
* Much faster traverses
* Much Faster snapshots
* New algorithm for flushing
* New vistNodes/visitLeaves
* Avoid I/O if a map is unbacked
New class RPC::Status enforces JSON-RPC 2.0 error format.

* Relevant issues:
  * RIPD-92
  * RIPD-97
  * RIPD-98
  * RIPD-439
Fix outgoing bytes calculation in HTTP server.
Call Stoppable::stopped in PeerFinder onStop.
Disable transaction submission tests under Travis.
Refactor SerializedTransaction:
* Use boost:tribool instead of two intertwined bool variables
* Trim down public interface, reduce member variables
Disable SSLv3
Remove boost_thread dependency (RIPD-216).

Fixes RIPD-216
Fix tabs and trailing whitespace.
Detab beast
Fix URL compositing in Beast (RIPD-636).