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

modules/beast_core/containers/PropertySet.cpp

@@ -21,6 +21,9 @@
 */
 //==============================================================================
 
+namespace beast
+{
+
 PropertySet::PropertySet (const bool ignoreCaseOfKeyNames)
     : properties (ignoreCaseOfKeyNames),
       fallbackProperties (nullptr),
@@ -216,3 +219,5 @@ void PropertySet::restoreFromXml (const XmlElement& xml)
 void PropertySet::propertyChanged()
 {
 }
+
+}  // namespace beast