Merge branch 'jk/patch-ids-no-merges'

"git log --cherry-pick" used to include merge commits as candidates
to be matched up with other commits, resulting a lot of wasted time.
The patch-id generation logic has been updated to ignore merges to
avoid the wastage.

* jk/patch-ids-no-merges:
  patch-ids: refuse to compute patch-id for merge commit
  patch-ids: turn off rename detection