Merge branch 'ks/combine-diff'

Teach combine-diff to honour the path-output-order imposed by diffcore-order, and optimize how matching paths are found in the N-way diffs made with parents. * ks/combine-diff: tests: add checking that combine-diff emits only correct paths combine-diff: simplify intersect_paths() further combine-diff: combine_diff_path.len is not needed anymore combine-diff: optimize combine_diff_path sets intersection diff test: add tests for combine-diff with orderfile diffcore-order: export generic ordering interface