Merge branch 'kw/patch-ids-optim'

When "git rebase" tries to compare set of changes on the updated upstream and our own branch, it computes patch-id for all of these changes and attempts to find matches. This has been optimized by lazily computing the full patch-id (which is expensive) to be compared only for changes that touch the same set of paths. * kw/patch-ids-optim: rebase: avoid computing unnecessary patch IDs patch-ids: add flag to create the diff patch id using header only data patch-ids: replace the seen indicator with a commit pointer patch-ids: stop using a hand-rolled hashmap implementation