[MERGE][#124325] Rename the .bzr.backup dir to .backup.bzr

[Ian Clatworthy]

Ian Clatworthy has voted tweak.
Status is now: Conditionally approved
Comment:
Discussing this with John further, I agree it ought to be named 
backup.bzr instead of .backup.bzr. Will tweak and merge.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C2422be180803040403y6873e4f0pa7fffe32551a12a1%40mail.gmail.com%3E