At the very beginning we reset the bufferevent fd (if bev has it), which
is not a good idea, since if user passes bufferevent with existing fd he
has some intention.
So we need to:
- use BEV_OPT_CLOSE_ON_FREE for default bufferevent_socket_new() (to
avoid manual shutdown/closee)
- drop getsockopt(SOL_SOCKET, SO_ERROR), since bufferevent already has
evutil_socket_finished_connecting_()
- drop supperior bufferevent_setfd(bev, -1) in
evhttp_connection_connect_()
Closes: #795
Refs: #875
afa66ea420