push and update does not work if the user does not have ssh, for example on Windows, where they might have plink

jam: glyph: it would be something like: vendor = bzrlib.transport.ssh._get_vendor()
jam: connection = vendor.connect_ssh(..., command=[bzr_remote_path, 'update', path)
jam: shouldn't be too hard to do

As a temporary solution for Win32 users, the attached .patch (against r10) should make push-and-update compatible with plink.exe. Please note that plink.exe must be in your PATH, and pageant.exe must be running. Tested only on Windows XP w/ python2.5.