[merge][rfc] small inventory apply_delta patch

[Martin Pool]

Martin Pool has voted resubmit.
Status is now: Resubmit
Comment:
This can't be merged as-is because of failing tests -- the base 
Inventory doesn't provide create_by_apply_delta (but probably should).

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3Ce01316480811102304s60b1df9cnf62aec9748a61346%40mail.gmail.com%3E
Project: Bazaar