Cherry-picked "evaluate" refactoring from dev-modernize branch

- fixed up NULL comparisons to allow for NULL being a long
- should address #981

include/internal/catch_expression_lhs.hpp

@@ -111,7 +111,7 @@ public:
 
     void endExpression() const {
         m_rb
-            .setResultType( Internal::compare<Op>( m_lhs, m_rhs ) )
+            .setResultType(  Internal::Evaluator<LhsT, RhsT, Op>::evaluate( m_lhs, m_rhs ) )
             .endExpression( *this );
     }