[MERGE] Change the smart server get_parents method to take a graph search to exclude already recieved parents from. This prevents history shortcuts causing huge numbers of duplicates.

[John Arbash Meinel]

Robert Collins wrote:
> Whee long titles.
> 
> So this patch changes the current bzr.dev-only Repository.get_parents
> smart server method, eliminating duplication and gzipping the content.
> 
> With 100 missing mainline revsions (659 in total to pull) this generates
> the parameters to stream in 8 seconds on a lon-syd pull, in 2 round
> trips.
> 
> Its not optimal; I have some ideas about that but want to get this into
> 1.2 - the optimal stuff will be a bit more of an overhaul of the overall
> fetch process to use branch information to [ideally] provide single
> round trips in a number of common cases (like first branch into a shared
> repo!).
> 
> -Rob

I feel like gzip should be done at a higher level, since HTTP supports 
transfer encodings and by default ssh also compresses the traffic. I've 
certainly considered doing it in the protocol level, but after thinking 
about it, it seems a bit better to do it elsewhere.

Also, if we are going to gzip, I would guess that bzip2 would be a 
better tradeoff for network requests.

John
=:->