Make the hurting stop.  Make sshxmlrpc auto-detect things, fails over
properly, and dump useful information when it is unable to deal with
the peer.

  * xmlrpc/sshxmlrpc.py: Major update.  It now tries to autoconfigure
    itself by scanning the path for "ssh" and "plink.exe" (although I
    haven't actually tried it on windows).  Environment variables can
    now be used to turn on debugging and set the command to use for
    doing the ssh.  Before running ssh, it will check for an agent or
    a passphrase-less key and prints a warning if it finds neither.
    The last five lines read from the server, as well as the standard
    error output, are stored so they can be dumped later; helpful for
    figuring out what is actually being run on the other side.  The
    protocol layer between ssh and xml-rpc will now respond to a
    "probe" header so that clients can figure out who they are talking
    too.  The server side will now properly detect a closed connection
    and not write anything, which means...