Fix conflicts for tracking revisions
    
    Currently, to track which step of the bisect we are on,
    EXTRAVERSION is used to hold the state, awk parses it out to update
    it, and git stash/pop are used before checkout of the next step.
    This works great until conflicts occur around the EXTRAVERSION either
    because EXTRAVERSION itself changed or the name or some other reason.
    Trying to save the state in EXTRAVERSION just leads to a bunch of
    unnecessary and awkard[1] parsing. Instead, save the step in an extra
    file. This way the step can be cleanly applied on each step even if
    the state changes
    
    [1] The awk pun was unintentional until after I wrote it.