Support for selecting AES from the GUI. In the process, I've had to

Support for selecting AES from the GUI. In the process, I've had to
introduce another layer of abstraction in SSH2 ciphers, such that a
single `logical cipher' (as desired by a user) can equate to more
than one `physical cipher'. This is because AES comes in several key
lengths (PuTTY will pick the highest supported by the remote end)
and several different SSH2-protocol-level names (aes*-cbc,
rijndael*-cbc, and an unofficial one rijndael-cbc@lysator.liu.se).

git-svn-id: svn://svn.tartarus.org/sgt/putty@967 cda61777-01e9-0310-a592-d414129be87e