remote-bzr: trivial cleanups

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
remote-bzr: trivial refactoring

No functional changes.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
remote-bzr: add custom method to find branches

The official method is incredibly inefficient and slow.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
remote-bzr: add option to specify branches

We might not want all the branches. And branch handling in bazaar is
rather tricky, so it's safer to simply specify them.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
remote-bzr: improve progress reporting

No need to manually count the revisions, and also, this would help to
iterate more properly.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
remote-bzr: iterate revisions properly

This way we don't need to store the list of all the revisions, which
doesn't seem to be very memory efficient with bazaar's design, for
whatever reason.

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