New utility script to parse an SSH packet dump and write out an

interpretation with some analysis done on it. The script will do its
own tracking of the set of open channels and their states, and its
output is in a one-line-per-packet format such that every distinct
channel has a unique identifier in it which should make it easy to
grep out all lines relating to that channel. The script also matches
up {CHANNEL,REQUEST}_{SUCCESS,FAILURE} to the requests that caused
them, by tracking a queue of requests in each direction per channel
and for global requests. Command-line options permit generating a
final dump of all channels ever known to the script and their various
ids and final state, and also dumping out the data transferred over
each channel in each direction.

Output is not complete, in the sense that some parameters in some
messages (e.g. pixel sizes in window-size specifications) are
deliberately omitted due to being boring, and the entire contents of
some messages (e.g. KEXINIT) are omitted because I haven't yet seen
any purpose in decoding them. Filling them in might be a useful thing,
although I'm inclined to think that the default should still be to
show only the potentially interesting stuff (e.g. still not pixel
sizes!) and enable the rest using a -v option.

Hopefully this should do a lot of the legwork in debugging issues in
which a channel mysteriously remains partially open and prevents PuTTY
closing.

git-svn-id: svn://svn.tartarus.org/sgt/putty@9457 cda61777-01e9-0310-a592-d414129be87e