General tidy and refactoring:

* Use nullptr (C++11) instead of NULL.
* Put each file into its own namespace declaration.
* Remove "using namespace" directives and add scope qualifiers.
* Control when beast's implementation of std::equal (C++14) is used.
* Tidy up some const declarations.

Conflicts:
	src/ripple_app/shamap/SHAMapSync.cpp
	src/ripple_app/tx/TransactionEngine.cpp

src/ripple/json/impl/Tests.cpp

@@ -18,9 +18,8 @@
 //==============================================================================
 
 namespace ripple {
-using namespace beast;
 
-class JsonCppTests : public UnitTest
+class JsonCppTests : public beast::UnitTest
 {
 public:
     void testBadJson ()
@@ -50,4 +49,4 @@ public:
 
 static JsonCppTests jsonCppTests;
 
-}
+}  // namespace ripple