Merge branch 'pw/sequencer-in-process-commit'

The sequencer infrastructure is shared across "git cherry-pick",
"git rebase -i", etc., and has always spawned "git commit" when it
needs to create a commit.  It has been taught to do so internally,
when able, by reusing the codepath "git commit" itself uses, which
gives performance boost for a few tens of percents in some sample
scenarios.

* pw/sequencer-in-process-commit:
  sequencer: run 'prepare-commit-msg' hook
  t7505: add tests for cherry-pick and rebase -i/-p
  t7505: style fixes
  sequencer: assign only free()able strings to gpg_sign
  sequencer: improve config handling
  t3512/t3513: remove KNOWN_FAILURE_CHERRY_PICK_SEES_EMPTY_COMMIT=1
  sequencer: try to commit without forking 'git commit'
  sequencer: load commit related config
  sequencer: simplify adding Signed-off-by: trailer
  commit: move print_commit_summary() to libgit
  commit: move post-rewrite code to libgit
  Add a function to update HEAD after creating a commit
  commit: move empty message checks to libgit
  t3404: check intermediate squash messages

Author: gitster

builtin/commit.c

@@ -43,7 +43,7 @@ int cmd_rebase__helper(int argc, const char **argv, const char *prefix)
 		OPT_END()
 	};
 
-	git_config(git_default_config, NULL);
+	sequencer_init_config(&opts);
 	git_config_get_bool("rebase.abbreviatecommands", &abbreviate_commands);
 
 	opts.action = REPLAY_INTERACTIVE_REBASE;

builtin/rebase--helper.c

@@ -208,7 +208,7 @@ int cmd_revert(int argc, const char **argv, const char *prefix)
 	if (isatty(0))
 		opts.edit = 1;
 	opts.action = REPLAY_REVERT;
-	git_config(git_default_config, NULL);
+	sequencer_init_config(&opts);
 	res = run_sequencer(argc, argv, &opts);
 	if (res < 0)
 		die(_("revert failed"));
@@ -221,7 +221,7 @@ int cmd_cherry_pick(int argc, const char **argv, const char *prefix)
 	int res;
 
 	opts.action = REPLAY_PICK;
-	git_config(git_default_config, NULL);
+	sequencer_init_config(&opts);
 	res = run_sequencer(argc, argv, &opts);
 	if (res < 0)
 		die(_("cherry-pick failed"));