remote-bzr: support the new 'force' option

Signed-off-by: Richard Hansen <rhansen@bbn.com>
Acked-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
transport-helper: add support to push symbolic refs

For example 'HEAD'.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>