[MERGE] Branch.iter_merge_sorted_revisions

[Ian Clatworthy]

Martin Albisetti wrote:
> In case it seems better, this is what we're using in loggerhead now
> instead of _old_get_graph. Still have to pass it through
> _strip_NULL_ghosts, but I don't know another way around this.
> Not sure if it's an improvement or not, but it does still pass all the tests  :)

Thanks. Applied.

Following poolie's review, I've submitted this to PQM now.
The API *may* change following more feedback though.

I've updated bzr-revnocache to load/save the graph in a cache if
Branch.iter_merge_sorted_revisions() exists & is called. You should
therefore be able to start using this API in Loggerhead and,
as long as the latest bzr-revnocache and a Real-Soon-Now
bzr.dev are installed, see a performance gain of some kind.

There's still plenty of tuning we can do in revnocache in
terms of better file formats, only saving changes since
the parent (& delegating to it for the rest), smarts around
moving the tip, etc. I'll gladly take any patches you can
offer. :-)

Ian C.