message: std::pair "last" -> "first" in http_message.qbk
  fix
diff: @@ -209,13 +209,13 @@ with arbitrary variadic lists of parameters. This allows the container
  to fully support allocators.
  The solution used in the library is to treat the message like a `std::pair`
  -for the purposes of construction, except that instead of `first` and `last`
  -we have `fields` and `body`. This means that single-argument constructors
  -for those fields should be accessible as they are with `std::pair`, and
  -that a mechanism identical to the pair's use of `std::piecewise_construct`
  -should be provided. Those constructors are too complex to repeat here, but
  -interested readers can view the declarations in the corresponding header
  -file.
  +for the purposes of construction, except that instead of `first` and `second`
  +we have the `Fields` base class and `message::body` member. This means that
  +single-argument constructors for those fields should be accessible as they
  +are with `std::pair`, and that a mechanism identical to the pair's use of
  +`std::piecewise_construct` should be provided. Those constructors are too
  +complex to repeat here, but interested readers can view the declarations
  +in the corresponding header file.
  There is now significant progress with our message container but a stumbling
  block remains. There is no way to control the allocator for the `std::string`
  