Invalide free for msgpack future.

[absolute8511]

After some review on the source code. I noticed the follow problem:

The auto_zone hold a object which is allocated by malloc.
See below:
line 325 in rpc/transport/base.h, the zone object passed to the on_message is from the m_pac.release_zone().
And this auto_zone will be passed to on_response in session_impl and then to the set_result in the future_impl.
The future_impl will hold this auto_zone until its destructor.

But the auto_ptr will use the delete not a free in reset() or destructor. I think this may be why the valgrind reports the invalid info.