After pushing at the end of "arc land", cascade the origin through all local tracking branches
Fixes T9661. Users can construct arbitrarily long chains from the remote, like:
(remote) origin/master -> (local) cascade-a -> (local) cascade-b -> (local) cascade-c -> (local) cascade-d
When a user lands "cascade-d" onto "origin/master", we should pull A, B and C if they aren't ahead of the remote.
If a user lands "cascade-d" onto itself, we should pull A, B, and C if they aren't ahead of the remote, then reset D to the remote.
We also find this chain if the last component of it is connected by the local branch having the same name as the remote branch (typical for "master") instead of an actual connection through tracking brnaches.
Test Plan: See comment below.
Reviewed By: chad
Maniphest Tasks: T9661
Differential Revision: https://secure.phabricator.com/D14361