more tests:
- Run all tests against repository with revprop changing allowed and without
- performance tests (count roundtrips?)
- reconcile

performance:
- use chk maps for file ids
- store changes root path in tdb cache, for quicker iter_changes().
- when walking history, also update revid cache if possible
 - and perhaps tags info?
 - and perhaps revno info ?
- fix copyfrom in replay and replay_range
- automatically disable cache in some situations, allow partial cache?
 - perhaps for large repositories?
- special LRU cache for revisionmetadata

for other things to do, see:

* https://bugs.launchpad.net/bzr-svn
