remote-bzr: remove stale check code for tests

The fastimport plugin was only required in the early stage of
development.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
remote-bzr: fix directory renaming

Git does not handle directories, renaming a directory is renaming every
files in this directory.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
remote-bzr: add directory move test

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
remote-bzr: remove files before modifications

Allow re-add of a deleted file in the same commit.

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