bdiff: normalize the diff (issue1295)
When the common part of a diff can be moved forward, move it forward.
Otherwise we don't get deterministic results (it would depends on the way we
split for the recursion).
That way we get identical hunks when doing the same change, it helps to solve
issue1295 (inconsistent diffs on different side during a merge).
% test multiple merges at once
initializing destination source-hg repository
scanning source...
sorting...
converting...
4 Initial add
3 Added branch1 file
2 Added parent file
1 Added brach2 file
0 Merged branches
o 5 "(octopus merge fixup)" files:
|\
| o 4 "Merged branches" files: file-branch2
| |\
o---+ 3 "Added brach2 file" files: file-branch2
/ /
| o 2 "Added parent file" files: file-parent
| |
o | 1 "Added branch1 file" files: file file-branch1
|/
o 0 "Initial add" files: file
% manifest of tip
644 file
644 file-branch1
644 file-branch2
644 file-parent