Build system improvements:

* Reduce console verbosity.
* Display configured build environment.
* Log build environment and commands in rippled-build.log.
* When compiling under Travis:
  - define TRAVIS_CI_BUILD for C and C++ code.
  - define RIPPLE_MASTER_BUILD for builds made against
    the official Ripple repository.
Fix SConstruct compiler arguments
beast, beast::asio improvements and fixes:
* New maybe_const_t alias for maybe_const
* New asio::enable_wait_for_async for safe cleanup
* New asio::memory_buffer, a managed boost::asio compatible buffer
* shared_handler improvements:
   - Can be 'empty' (no stored handler).
   - Default constructible as 'empty'.
   - Safe evaluation in bool contexts, false==empty
* Fix is_call_possible metafunction:
   - Works on empty argument lists
   - Works with reference types
* Replace SafeBool idiom with C++11 explicit operator bool
* Move IPAddress function definitions to the header
* Move cyclic_iterator to container/
* Remove unused BufferType
* Remove obsolete classes:
   - NamedPipe
   - ReadWriteLock
   - ScopedReadLock
   - ScopedWriteLock
   - LockGuard
Refactor ECDSA canonical checks
[FOLD] Fix typo
[FOLD/TX-REFAC] Transactor include guard fixup
[FOLD/TX-REFAC] WalletAdd Transactor journal
[FOLD/TX-REFAC] TrustSet Transactor journal
[FOLD/TX-REFAC] RegularKeySet Transactor journal
[FOLD/TX-REFAC] Payment Transactor journal
[FOLD/TX-REFAC] OfferCancel Transactor journal
[FOLD/TX-REFAC] Change Transactor journal
[FOLD/TX-REFAC] AccountSet Transactor journal
[FOLD/TX-REFAC] OfferCreate Transactor journal