fix#1202
Replace them by their cousins from std::allocator_traits;
otherwise, heaps of deprecation warnings will fall onto
humble users when compiling with MSVC 15 in C++17 mode.
Signed-off-by: Daniela Engert <dani@ngrt.de>
The ssl_stream wrapper provides C++11 move semantics for ssl::stream,
as well as incorporating the flat_stream workaround for a performance
problem with ssl::stream writes and buffer sequences having length
greater than one.