Now that Packet structures are dynamically allocated, it means we

Now that Packet structures are dynamically allocated, it means we
can keep several of them in parallel. In particular, this allows us
to queue outgoing packets during repeat key exchange, to be actually
sent after the rekey completes.

(This doesn't fully fix ssh2-kex-data; also required is the ability
to handle _incoming_ connection-layer packets during rekey without
exploding.)

[originally from svn r4899]