bisect: stop early if we find a perfect candidate

bisect: find best node in ancestor collection pass

bisect: calculate candidate set while finding children

bisect: use a dict for children We fill in the children only for ancestors of badrev

bisect: propagate ancestor lists directly to children - calculate the children of all candidates - for each candidate, combine ancestor lists - pass ancestor lists to children - store ancestor count This eliminates the O(n**2) memory usage, while maintaining about the same performance.

bisect: add noupdate option

Merge backout

Backed out changeset c2a21fe60994 Unfortunately, this breaks backward compatibility.