Update dropbear to 0.52.  Build an scp binary and call it dbscp so it
doesn't conflict with openssh.

Changes since 0.50:

0.52 - Wed 12 November 2008

- Add "netcat-alike" option (-B) to dbclient, allowing Dropbear to
  tunnel standard input/output to a TCP port-forwarded remote host.

- Add "proxy command" support to dbclient, to allow using a spawned
  process for IO rather than a direct TCP connection. eg
  dbclient remotehost
  is equivalent to
  dbclient -J 'nc remotehost 22' remotehost
  (the hostname is still provided purely for looking up saved host keys)

- Combine netcat-alike and proxy support to allow "multihop"
  connections, with comma-separated host syntax.  Allows running

  dbclient user1@host1,user2@host2,user3@host3

  to end up at host3 via the other two, using SSH TCP forwarding. It's
  a bit like onion-routing. All connections are established from the
  local machine.  The comma-separated syntax can also be used for
  scp/rsync, eg

  rsync -a -e dbclient m@gateway,m2@host,martello:/home/matt/ ~/backup/

  to bounce through a few hosts.

- Add -I "idle timeout" option (contributed by Farrell Aultman)

- Allow restrictions on authorized_keys logins such as restricting
  commands to be run etc. This is a subset of those allowed by OpenSSH,
  doesn't yet allow restricting source host.

- Use vfork() for scp on uClinux

- Default to PATH=/usr/bin:/bin for shells.

- Report errors if -R forwarding fails

- Add counter mode cipher support, which avoids some security problems
  with the standard CBC mode.

- Support zlib@openssh.com delayed compression for client/server. It
  can be required for the Dropbear server with the '-Z' option. This
  is useful for security as it avoids exposing the server to attacks
  on zlib by unauthenticated remote users, though requires client side
  support.

- options.h has been split into options.h (user-changable) and
  sysoptions.h (less commonly changed)

- Support "dbclient -s sftp" to specify a subsystem

- Fix a bug in replies to channel requests that could be triggered by
  recent versions of PuTTY

0.51 - Thu 27 March 2008

- Make a copy of password fields rather erroneously relying on getwpnam()
  to be safe to call multiple times

- If $SSH_ASKPASS_ALWAYS environment variable is set (and $SSH_ASKPASS is
  as well) always use that program, ignoring isatty() and $DISPLAY

- Wait until a process exits before the server closes a connection, so
  that an exit code can be sent. This fixes problems with exit codes not
  being returned, which could cause scp to fail.

(snj)