tests/test-dirstatedirs.out

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.

adding a/b/c/d/x
adding a/b/c/d/y
adding a/b/c/d/z
moving a/b/c/d/x to z/b/c/d/x
moving a/b/c/d/y to z/b/c/d/y
moving a/b/c/d/z to z/b/c/d/z