Specific comparison operators

In case we want to turn operator== into a free function, this will
prevent premature instantiation of wrap_operand

include/sqlpp11/data_types/day_point/operand.h

@@ -61,7 +61,7 @@ namespace sqlpp
 
     bool _is_trivial() const
     {
-      return _t == _value_t{};
+      return std::chrono::operator==(_t, _value_t{});
     }
 
     _value_t _t;

include/sqlpp11/data_types/time_point/operand.h

@@ -62,7 +62,7 @@ namespace sqlpp
 
     bool _is_trivial() const
     {
-      return _t == _value_t{};
+      return std::chrono::operator==(_t, _value_t{});
     }
 
     _value_t _t;