remote-bzr: fix directory renaming

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

[fc: added tests]

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>
remote-bzr: set author if available

[fc: added tests]

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