Comment 4 for bug 402657

The attached branch fixes this by adding some batching, at least for the originally reported case of "bzr branch http://bazaar.launchpad.net/~launchpad-pqm/launchpad/devel".

It's still not 100% optimal (e.g. the continual re-read of the pack file format string on every single readv). And the batching is limited by what the requested stream ordering allows. For ordering='unordered', as in the originally reported case, it makes a big difference. For other operations that use other orderings we may still have more work to do. I suggest we file new, specific bug reports for these cases, if we find any.