Chunk commits by date in lists

It's possible to construct a commit graph where the output of `git log`
isn't in timestamp order. Grouping the commits in the list by date then
gives dramatically wrong results. Instead, go for the more pragmatic
approach: use the commits in the order they're given, and just show the
date line each time the date changes. This means that the same date
header can show up multiple times, but at least the ordering is
preserved.

CHANGELOG

@@ -43,7 +43,7 @@ v 8.8.0 (unreleased)
   - Add support for supressing text diffs using .gitattributes on the default branch (Matt Oakes)
   - Add eager load paths to help prevent dependency load issues in Sidekiq workers. !3724
   - Added multiple colors for labels in dropdowns when dups happen.
-  - Always group commits by server timezone, not commit timestamp
+  - Show commits in the same order as `git log`
   - Improve description for the Two-factor Authentication sign-in screen. (Connor Shea)
   - API support for the 'since' and 'until' operators on commit requests (Paco Guzman)
   - Fix Gravatar hint in user profile when Gravatar is disabled. !3988 (Artem Sidorenko)

app/views/projects/commits/_commits.html.haml

@@ -3,7 +3,7 @@
 
 - commits, hidden = limited_commits(@commits)
 
-- commits.group_by { |c| c.committed_date.in_time_zone.to_date }.sort.reverse.each do |day, commits|
+- commits.chunk { |c| c.committed_date.in_time_zone.to_date }.each do |day, commits|
   .row.commits-row
     .col-md-2.hidden-xs.hidden-sm
       %h5.commits-row-date