bdiff: give slight preference to appending lines [This change could be folded into the previous changeset to minimize the repo churn ...] The general preference to matches in the middle of bdiff ranges helps getting balanced recursion and efficient computation. But, as previous changes have shown, it might also give diffs that seems "obviously wrong". To mitigate that: If the best match on the A side starts at the beginning of the bdiff range, don't aim for the middle-most B side match but for the earliest. This will make the matches balanced (by both sides being "early") even though the bisection will be less balanced. Still, this case only apply if the *best* and middle-most match was fully unbalanced on the A side. Each recursion will thus even in this worst case reduce the problem significantly and we are not re-introducing the problem that was fixed in f1ca249696ed. The bundle size for 4.0 (hg bundle --base null -r 4.0 x.hg) happens to go from 22806817 to 22807275 bytes - a 0.002% increase. This make the recent test-bdiff.py changes give a more pretty output ... but they no longer show that the recursion is around middle matches (because it in these cases isn't).