def within_history(rev, windowdict):
    """Return whether the windowdict has history at the revision."""
    if not windowdict:
        return False
    begin = windowdict._past[0][0] if windowdict._past else \
            windowdict._future[-1][0]
    end = windowdict._future[0][0] if windowdict._future else \
          windowdict._past[-1][0]
    return begin <= rev <= end
Return whether the windowdict has history at the revision.