[MERGE] Significantly reducing execution time and network traffic for trivial case of `bzr missing`

[John Arbash Meinel]

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Alexander Belchenko wrote:
| Running `bzr missing http://bzrdev.bialix.com/fast-missing/`
| from local mirror of fast-missing branch (i.e. branches are identical)
| with bzr 1.2
| I get:
|
| data received: 2135 KB
| data sent: 60 KB
| execution time: 191.094 seconds
|
| With this patch I get:
|
| data received: 5 KB
| data sent: 3 KB
| execution time: 7.875 seconds.
|

I think there are better ways of doing this by using the Graph functionality. If
'find_differences()' was actually correct it would be a trivial:

graph = local_branch.repository.get_graph(remote_branch.repository)
left_revno, left_revision_id = local_branch.last_revision_info()
right_revno, right_revision_id = remote_branch.last_revision_info()
(left, right) = graph.find_differences(left_revision_id, right_revision_id)

However, as it still needs to call last_revision_info, we can easily slot in
your change here.

So....

BB:approve

John
=:->
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