show-branch --reflog: show the reflog message at the top.

show-branch --reflog: show the reflog message at the top.

This changes the output so the list at the top shows the reflog
message, along with their relative timestamps.

You can use --reflog=<n> to show <n> most recent log entries, or
use --reflog=<n>,<b> to show <n> entries going back from the
entry <b>.  <b> can be either a number (so --reflog=4,20 shows 4
records starting from @{20}) or a timestamp (e.g. --reflog='4,1 day').

Here is a sample output (with --list option):

  $ git show-branch --reflog=10 --list jc/show-reflog
    [jc/show-reflog@{0}] (3 minutes ago) commit (amend): show-branch --ref
    [jc/show-reflog@{1}] (5 minutes ago) reset HEAD^
    [jc/show-reflog@{2}] (14 minutes ago) commit: show-branch --reflog: sho
    [jc/show-reflog@{3}] (14 minutes ago) commit: show-branch --reflog: sho
    [jc/show-reflog@{4}] (18 minutes ago) commit (amend): Extend read_ref_a
    [jc/show-reflog@{5}] (18 minutes ago) commit (amend): Extend read_ref_a
    [jc/show-reflog@{6}] (18 minutes ago) commit (amend): Extend read_ref_a
    [jc/show-reflog@{7}] (18 minutes ago) am: read_ref_at(): allow retrievi
    [jc/show-reflog@{8}] (18 minutes ago) reset --hard HEAD~4
    [jc/show-reflog@{9}] (61 minutes ago) commit: show-branch --reflog: use

This shows what I did more cleanly:

  $ git show-branch --reflog=10 jc/show-reflog
  ! [jc/show-reflog@{0}] (3 minutes ago) commit (amend): show-branch --ref
   ! [jc/show-reflog@{1}] (5 minutes ago) reset HEAD^
    ! [jc/show-reflog@{2}] (14 minutes ago) commit: show-branch --reflog:
     ! [jc/show-reflog@{3}] (14 minutes ago) commit: show-branch --reflog:
      ! [jc/show-reflog@{4}] (18 minutes ago) commit (amend): Extend read_
       ! [jc/show-reflog@{5}] (18 minutes ago) commit (amend): Extend read
        ! [jc/show-reflog@{6}] (18 minutes ago) commit (amend): Extend rea
         ! [jc/show-reflog@{7}] (18 minutes ago) am: read_ref_at(): allow
          ! [jc/show-reflog@{8}] (18 minutes ago) reset --hard HEAD~4
           ! [jc/show-reflog@{9}] (61 minutes ago) commit: show-branch --r
  ----------
  +          [jc/show-reflog@{0}] show-branch --reflog: show the reflog
    +        [jc/show-reflog@{2}] show-branch --reflog: show the reflog
   +++       [jc/show-reflog@{1}] show-branch --reflog: show the reflog
  +++++      [jc/show-reflog@{4}] Extend read_ref_at() to be usable fro
       +     [jc/show-reflog@{5}] Extend read_ref_at() to be usable fro
        +    [jc/show-reflog@{6}] Extend read_ref_at() to be usable fro
         +   [jc/show-reflog@{7}] read_ref_at(): allow retrieving the r
           + [jc/show-reflog@{9}] show-branch --reflog: use updated rea
           + [jc/show-reflog@{9}^] read_ref_at(): allow reporting the c
           + [jc/show-reflog@{9}~2] show-branch --reflog: show the refl
           + [jc/show-reflog@{9}~3] read_ref_at(): allow retrieving the
  ++++++++++ [jc/show-reflog@{8}] dwim_ref(): Separate name-to-ref DWIM

At @{9}, I had a commit to complete 5 patch series, but I wanted
to consolidate two commits that enhances read_ref_at() into one
(they were @{9}^ and @{9}~3), and another two that touch show-branch
into one (@{9} and @{9}~2).

I first saved them with "format-patch -4", and then did a reset
at @{8}.  At @{7}, I applied one of them with "am", and then
used "git-apply" on the other one, and amended the commit at
@{6} (so @{6} and @{7} has the same parent).  I did not like the
log message, so I amended again at @{5}.

Then I cherry-picked @{9}~2 to create @{3} (the log message
shows that it needs to learn to set GIT_REFLOG_ACTION -- it uses
"git-commit" and the log entry is attributed for it).  Another
cherry-pick built @{2} out of @{9}, but what I wanted to do was
to squash these two into one, so I did a "reset HEAD^" at @{1}
and then made the final commit by amending what was at the top.

Signed-off-by: Junio C Hamano <junkio@cox.net>