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/validators/impl/SourceURL.h

@@ -27,7 +27,7 @@ namespace Validators {
 class SourceURL : public Source
 {
 public:
-    static SourceURL* New (URL const& url);
+    static SourceURL* New (beast::URL const& url);
 };
 
 }