Code review comment for lp://staging/~jelmer/bzr/hpss-get-inventories

Timings when checking out bzr.dev:

~/src/bzr/hpss-get-inventories/bzr co --lightweight bzr://people.samba.org/bzr.dev 2.25s user 0.46s system 15% cpu 17.277 total
~/src/bzr/hpss-get-inventories/bzr export /tmp/bzr.dev2 bzr://people.samba.org/bzr.dev 1.54s user 0.40s system 12% cpu 15.435 total

versus against an older bzr server:

~/src/bzr/hpss-get-inventories/bzr co --lightweight bzr://people.samba.org/bzr.dev 4.91s user 1.03s system 10% cpu 58.807 total
~/src/bzr/hpss-get-inventories/bzr export /tmp/bzr.dev5 bzr://people.samba.org/bzr.dev 4.35s user 0.98s system 9% cpu 58.357 total