push and pull on bound branches use too much network

[Robert Collins]

currently pull on a bound branch does the following:

given a source(maybe-remote), a checkout (which is local) and a
master(maybe-remote) of the checkout-
 * pulls from source to master - data travels over the wire twice
(source to bzr, bzr to master).
 * pulls from master to checkout - data travels over the wire once
(master to bzr, bzr to local disk).

For a total of three traversals of the repository data over the wire.
This should be:
 * fetch from source to checkout repository
 * fetch from checkout repository to master
 * update master branch last-revision
 * update local branch last-revision.

Likewise push currently does:
 given a source(local), checkout(maybe remote), and a master(maybe
remote) of the checkout-
 * pull from source to master (data crosses wire once)
 * pull from master to checkout (data crosses wire twice)

where it should do
 * pull from source to master
 * pull from source to checkout

This is using pull in the 0.14 API sense, before the current work I'm
doing to split pull and push into specific API calls.

 affects bzr
 status confirmed
 importance medium
-Rob

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