shrink-revlog: add "reverse postorder" and "postorder reverse" toposorts.
Based on a patch by Benoit Boissinot, adapted to the pluggable sort
algorithm design. toposort_reversepostorder() is a very good
performer; it's designed to recreate what the revlog would have looked
like if Mercurial had parent deltas now. toposort_postorderreverse()
is unstable and very inconsistent, but perhaps with some work it could
be made better.
shrink-revlog: instrument sort code to record statistics.
Notably, count "suboptimal" nodes (predecessor is not first parent)
and (with -v) report them at the end of the run.
convert: handle svn tree with empty roots (
issue2079)