ignore backup.bzr

[Marius Kruger]

In the past the backup folder (after an upgrade), was called .bzr.backup or some hidden file,
which was in the list of ignored files by default.

Now after I upgraded and didn't delete the backup.bzr folder,
if I add a bunch of files and then want to run `bzr add`, it adds the backup.bzr folder :(
I think this should be in the ignore list by default.

[Marius Kruger (amanica)]

I'm thinking that we should name the backups like the backups when we revert files,
then we won't have the problem of upgrades failing when an old backup exists and because they end in ~ I think they are implicitly ignored too.

[Martin Pool (mbp)]

yay parthm