sequencer: support amending commits

This teaches the sequencer_commit() function to take an argument that
will allow us to implement "todo" commands that need to amend the commit
messages ("fixup", "squash" and "reword").

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

sequencer.c

@@ -468,7 +468,7 @@ static char **read_author_script()
  * (except, of course, while running an interactive rebase).
  */
 int sequencer_commit(const char *defmsg, struct replay_opts *opts,
-			  int allow_empty, int edit)
+			  int allow_empty, int edit, int amend)
 {
 	char **env = NULL;
 	struct argv_array array;
@@ -498,6 +498,8 @@ int sequencer_commit(const char *defmsg, struct replay_opts *opts,
 	argv_array_push(&array, "commit");
 	argv_array_push(&array, "-n");
 
+	if (amend)
+		argv_array_push(&array, "--amend");
 	if (opts->gpg_sign)
 		argv_array_pushf(&array, "-S%s", opts->gpg_sign);
 	if (opts->signoff)
@@ -778,7 +780,7 @@ static int do_pick_commit(enum todo_command command, struct commit *commit,
 	}
 	if (!opts->no_commit)
 		res = sequencer_commit(git_path_merge_msg(), opts, allow,
-			opts->edit);
+			opts->edit, 0);
 
 leave:
 	free_message(commit, &msg);

sequencer.h

@@ -45,7 +45,7 @@ int sequencer_rollback(struct replay_opts *opts);
 int sequencer_remove_state(struct replay_opts *opts);
 
 int sequencer_commit(const char *defmsg, struct replay_opts *opts,
-			  int allow_empty, int edit);
+			  int allow_empty, int edit, int amend);
 
 extern const char sign_off_header[];