Code review comment for lp://staging/~mbp/bzr/135234-checkout-relpath

Aaron raises a question in https://bugs.edge.launchpad.net/bzr/+bug/135234/comments/4 as to whether it's really ideal to store relative paths all the time.

We do as a general principle store relative paths when possible, partly because they're more likely to work when the same directories are addressed across different transports.