Fix notifications and refreshing the cached merge status upon updates
    
    Basically, before this commit, when we pushed a new commit to the git
    repo, we would update all the open pull-requests involved with this
    branch so that we can link them to tickets, then we would refresh all
    the open pull-requests of the project (ie: clear out their cached merge
    status).
    With this commit, before we link PRs to ticket, we refresh them, so it
    sends notifications about rebase to the configured bus (if any) and
    comments about it in the UI. This process also refreshes the cached
    merge status.
    So we have to be careful not to clear this updated cached merge status
    later otherwise we updated it for nothing.
    So this commit ensures we only clear cached merge status of PRs we have
    not refreshed manually.
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>