Add BOOST_NULLPTR helper macro

doc/macro_reference.qbk

@@ -966,6 +966,10 @@ and must be defined for all translation units in the program, including Boost li
 This macro will no longer have any effect once an official Microsoft
 release supports the CTP features.
 ]]
+[[`BOOST_NULLPTR`][
+If `BOOST_NO_CXX11_NULLPTR` is not defined (i.e. C++11 compliant compilers), expands to `nullptr`,
+otherwise expands to `0`.
+]]
 ]
 
 [endsect]

include/boost/config/detail/suffix.hpp

@@ -1069,6 +1069,12 @@ namespace std{ using ::type_info; }
 
 #define BOOST_STATIC_CONSTEXPR  static BOOST_CONSTEXPR_OR_CONST
 
+#if !defined(BOOST_NO_CXX11_NULLPTR)
+# define BOOST_NULLPTR nullptr
+#else
+# define BOOST_NULLPTR 0
+#endif
+
 //
 // Set BOOST_HAS_STATIC_ASSERT when BOOST_NO_CXX11_STATIC_ASSERT is not defined
 //

test/helper_macro_test.cpp

@@ -62,6 +62,10 @@ struct trait
    enum { value = b };
 };
 
+void* test_nullptr()
+{
+   return BOOST_NULLPTR;
+}
 
 int main()
 {
@@ -82,6 +86,8 @@ int main()
       {
          result += 2;
       }
+
+      test_nullptr();
    }
    catch(int)
    {