Merge branch 'lc/rebase-trailer' into seen

Refactor code paths to run "interpret-trailers" from "git
commit/tag" and use it in "git rebase".

Comments?

* lc/rebase-trailer:
  rebase: support --trailer
  trailer: append trailers in-process and drop the fork to `interpret-trailers`
  trailer: move process_trailers to trailer.h
  interpret-trailers: factor out buffer-based processing to process_trailers()

diff --cc builtin/commit.c
Simple merge

diff --cc builtin/tag.c
Simple merge

diff --cc sequencer.c
Simple merge

diff --cc t/meson.build
index 4e070cbbf7457fc7a7f41b8ee68f47dbe3db556f,56bc3291ced13efe36f6f5557566e47f0b258a3c..358477fbfcd586c3800f83b5ab25d19df4661fe0
--- 1/t/meson.build
--- 2/t/meson.build
+++ b/t/meson.build
@@@ -385,9 -385,7 +385,10 @@@ integration_tests = 
    't3436-rebase-more-options.sh',
    't3437-rebase-fixup-options.sh',
    't3438-rebase-broken-files.sh',
+   't3440-rebase-trailer.sh',
 +  't3450-history.sh',
 +  't3451-history-reword.sh',
 +  't3452-history-split.sh',
    't3500-cherry.sh',
    't3501-revert-cherry-pick.sh',
    't3502-cherry-pick-merge.sh',