GenericValue: use IsBaseOf to support comparisons between Value/Document

This finally fixes #113.

include/rapidjson/document.h

@@ -683,7 +683,7 @@ public:
     //! Equal-to operator with primitive types
     /*! \tparam T Either \ref Type, \c int, \c unsigned, \c int64_t, \c uint64_t, \c double, \c true, \c false
     */
-    template <typename T> RAPIDJSON_DISABLEIF_RETURN((internal::IsPointer<T>), (bool)) operator==(const T& rhs) const { return *this == GenericValue(rhs); }
+    template <typename T> RAPIDJSON_DISABLEIF_RETURN((internal::OrExpr<internal::IsPointer<T>,internal::IsBaseOf<GenericValue,T> >), (bool)) operator==(const T& rhs) const { return *this == GenericValue(rhs); }
 
     //! Not-equal-to operator
     /*! \return !(*this == rhs)
@@ -693,17 +693,17 @@ public:
     //! Not-equal-to operator with arbitrary types
     /*! \return !(*this == rhs)
      */
-    template <typename T> bool operator!=(const T& rhs) const { return !(*this == rhs); }
+    template <typename T> RAPIDJSON_DISABLEIF_RETURN((internal::IsBaseOf<GenericValue,T>), (bool)) operator!=(const T& rhs) const { return !(*this == rhs); }
 
     //! Equal-to operator with arbitrary types (symmetric version)
     /*! \return (rhs == lhs)
      */
-    template <typename T> friend bool operator==(const T& lhs, const GenericValue& rhs) { return rhs == lhs; }
+    template <typename T> friend RAPIDJSON_DISABLEIF_RETURN((internal::IsBaseOf<GenericValue,T>), (bool)) operator==(const T& lhs, const GenericValue& rhs) { return rhs == lhs; }
 
     //! Not-Equal-to operator with arbitrary types (symmetric version)
     /*! \return !(rhs == lhs)
      */
-    template <typename T> friend bool operator!=(const T& lhs, const GenericValue& rhs) { return !(rhs == lhs); }
+    template <typename T> friend RAPIDJSON_DISABLEIF_RETURN((internal::IsBaseOf<GenericValue,T>), (bool)) operator!=(const T& lhs, const GenericValue& rhs) { return !(rhs == lhs); }
     //@}
 
     //!@name Type