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