Merge #16223: devtools: Fetch and display ACKs at sign-off time in github-merge

0e01e4522e devtools: Fetch and display ACKs at sign-off time in github-merge (Wladimir J. van der Laan)

Pull request description:

  - Fetch the ACKs only at sign-off time. This makes sure that any last-minute ACKs are included (fixes #16200)
  - Show a list of ACKs that will be included and their author before signing off, and warn if there are none

  ![1](https://user-images.githubusercontent.com/126646/59605250-ad070980-910e-11e9-9f9a-d789c7f06ebb.png)
  ![2](https://user-images.githubusercontent.com/126646/59605255-b1332700-910e-11e9-80a5-d1e244f48264.png)

  There's a slight change to the merge commit format—before it was
  ```
      ACKs for commit 88884c:
  (list of ACKs, could be empty)
  ```
  now it is
  ```
  ACKs for top commit:
        jnewbery:
          ACK 5ebc6b0eb
      ... (list of ACKs cannot be empty)
  ```
  or
  ```
  Top commit has no ACKs.
  ```
  I don't think there's a reason to have the abbreviated commit ID there, after all the full commit id is already in the beginning of the merge commit message, and at least the abbreviated one is in every single ACK message.

ACKs for commit 0e01e4:
  fanquake:
    ACK 0e01e4522e0f9e2e994f80fc61f40d61a4a70d79

Tree-SHA512: 8576de016137d71cfc101747e9bb6779c13e0953cf2babee7afc9972bf2bd46f6912be4982b54fa5abf4d91e98e8fdae6b4ca3eef7d6892b7a5f04a7017b6882

0 files changed, 0 insertions, 0 deletions