RFR: 1452: Can never notify on first commit [v7]

[Zhao Song]

> I changed the logic when there is no notify history.
> 
> Originally, on the first commit of a new repo, the bot would find no notify history, so it will make the first commit as an initial state and it will not make any notification.
> 
> Now, on the first commit of a new repo, the bot would find no notify history too, but it will make the initial git hash as the initial state of the repo, so it will treat the first commit as an 'update' operation and will make notifications.

Zhao Song has updated the pull request incrementally with two additional commits since the last revision:

 - fix a bug
 - add a method ReadOnlyRepository#initialHash

-------------

Changes:
  - all: https://git.openjdk.org/skara/pull/1385/files
  - new: https://git.openjdk.org/skara/pull/1385/files/feff1dbc..5be09539

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1385&range=06
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1385&range=05-06

  Stats: 23 lines in 5 files changed: 19 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/skara/pull/1385.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1385/head:pull/1385

PR: https://git.openjdk.org/skara/pull/1385