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

beast/cxx14/algorithm.h

@@ -25,6 +25,8 @@
 
 #include <algorithm>
 
+#if ! BEAST_NO_CXX14_EQUAL
+
 namespace std {
 
 namespace detail {
@@ -88,3 +90,5 @@ bool equal (FwdIt1 first1, FwdIt1 last1,
 }
 
 #endif
+
+#endif