sequencer: make three functions and an enum from sequencer.c public

This makes rebase_path_todo(), get_missing_commit_check_level(),
write_message() and the enum check_level accessible outside sequencer.c,
renames check_level to missing_commit_check_level, and prefixes its
value names by MISSING_COMMIT_ to avoid namespace pollution.

This function and this enum will eventually be moved to
rebase-interactive.c and become static again, so no special attention
was given to the naming.

This will be needed for the rewrite of append_todo_help() from shell to
C, as it will be in a new library source file, rebase-interactive.c.

Signed-off-by: Alban Gruin <alban.gruin@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sequencer.h

@@ -3,6 +3,7 @@
 
 const char *git_path_commit_editmsg(void);
 const char *git_path_seq_dir(void);
+const char *rebase_path_todo(void);
 
 #define APPEND_SIGNOFF_DEDUP (1u << 0)
 
@@ -57,6 +58,15 @@ struct replay_opts {
 };
 #define REPLAY_OPTS_INIT { .action = -1, .current_fixups = STRBUF_INIT }
 
+enum missing_commit_check_level {
+	MISSING_COMMIT_CHECK_IGNORE = 0,
+	MISSING_COMMIT_CHECK_WARN,
+	MISSING_COMMIT_CHECK_ERROR
+};
+
+int write_message(const void *buf, size_t len, const char *filename,
+		  int append_eol);
+
 /* Call this to setup defaults before parsing command line options */
 void sequencer_init_config(struct replay_opts *opts);
 int sequencer_pick_revisions(struct replay_opts *opts);
@@ -79,6 +89,7 @@ int sequencer_make_script(FILE *out, int argc, const char **argv,
 
 int sequencer_add_exec_commands(const char *command);
 int transform_todos(unsigned flags);
+enum missing_commit_check_level get_missing_commit_check_level(void);
 int check_todo_list(void);
 int skip_unnecessary_picks(void);
 int rearrange_squash(void);