Improvements to SConstruct:
* Default target is release instead of debug (scons with no arguments).
* All targets now include debug symbols, including release.
Rationale: "out of the box" builds of rippled using plain "scons" or "scons -j4" will produce
a debug instead of a release build, which could underperform.
Build gcc.debug using -Og flag

Since gcc 4.8 is required anyways, it might be nice to use its features.

Intro to feature (second bullet point):
https://gcc.gnu.org/gcc-4.8/changes.html

-g (line 328) is still needed:
http://stackoverflow.com/questions/12970596/gcc-4-8-does-og-imply-g
Add +DEBUG to the raw version string for DEBUG builds.
This will show up in the rpc server_info command.
There is no impact on the version string for release builds.
Mark several Ledger member functions as const.
Decouple LedgerMaster from configuration
Distinguish Byzantine failure from tx bug (RIPD-523)
Return correct error message for invalid fields
Add --quorum command line argument (RIPD-563)
Make path filtering smarter (RIPD-561)
* Break path liquidity checking into its own function
* Measure initial quality over minimum destination amount
* Test for available liquidity
Config improvements:
* More fine-grained Section mutators
* Add remap for mapping legacy single sections to key value pairs
* Add output stream operators for BasicConfig and Section
* Allow section values to be overwritten from command line
* Update rpc key/value configs from command line
* Add RPC::Setup with defaults and remap legacy rpc sections
Use secure RPC connections when configured
Remove obsolete SharedArg
Rewrite HTTP/S server to use coroutines:
* Fix bug with more than one complete request in a read buffer
* Use stackful coroutines for simplified control flow
* Door refactored to detect handshakes
* Remove dependency on MultiSocket
* Remove dependency on handshake detect logic framework
Consume handshake data in HTTP/S server
Use trusted validators median fee

Conflicts:
	src/ripple/app/misc/Validations.cpp
Use deleted members to prevent copying in rippled (RIPD-268)
Use deleted members to prevent copying in Beast (RIPD-268)
Use namespaces instead of static-only classes
Remove unused testoverlay module
Improve BuildInfo interface:
* Remove unnecessary beast::String dependency
* Explicitly cast to result type while packing a version
* Add unit tests for version formatting