ssh.com 3.2.0 uses zlib sync flush (start and close an empty

ssh.com 3.2.0 uses zlib sync flush (start and close an empty
uncompressed block at the end of each compressed packet) which we
were embarrassingly unable to deal with because we assumed every
uncompressed block contained at least one byte. Particularly silly
because I _knew_ about the existence of sync flush when I coded this
module. Arrgh. Still, now fixed.

[originally from svn r1824]