[PATCH 1 of 1] sshserver: add varargs capability

[Sune Foldager]

I made some more updates to
http://mercurial.selenic.com/wiki/WireProtocolUnificationPlan
recently.

We're going to need server capabilities to make any changes in the wire
protocol both for ssh (adding flexible arguments) and http (adding oob
error stream). My initial patch dealt with ssh in a simple way (no JSON
or similar) and called the capability 'varargs'. We may want to go with
a different name instead, such as a protocol version number; maybe
"v1.1" or whatever system we can come up with.

I realize http already transmits something like that back, although I am
not sure it's actually meant to be a version number. Due to the
stateless nature, we need to send it with all commands, OR the server
needs to be able to figure out the version from the command sent. This
is the case for my ssh patch; the server can see the difference.

/Sune