prefer comment_line_str to comment_line_char for printing

As part of our transition to multi-byte comment characters, we should
use the string variable rather than the historical character variable.
All of the sites adjusted here are just swapping out "%c" for "%s" in
format strings, or strbuf_addch() for strbuf_addstr(). The type system
and printf-attribute give the compiler enough information to make sure
our formats and variable changes all match (especially important for
cases where the format string is defined far away from its use, like
prepare_to_commit() in commit.c).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/commit.c b/builtin/commit.c
index 583bf04..e04f123 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -910,18 +910,18 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 		struct ident_split ci, ai;
 		const char *hint_cleanup_all = allow_empty_message ?
 			_("Please enter the commit message for your changes."
-			  " Lines starting\nwith '%c' will be ignored.\n") :
+			  " Lines starting\nwith '%s' will be ignored.\n") :
 			_("Please enter the commit message for your changes."
-			  " Lines starting\nwith '%c' will be ignored, and an empty"
+			  " Lines starting\nwith '%s' will be ignored, and an empty"
 			  " message aborts the commit.\n");
 		const char *hint_cleanup_space = allow_empty_message ?
 			_("Please enter the commit message for your changes."
 			  " Lines starting\n"
-			  "with '%c' will be kept; you may remove them"
+			  "with '%s' will be kept; you may remove them"
 			  " yourself if you want to.\n") :
 			_("Please enter the commit message for your changes."
 			  " Lines starting\n"
-			  "with '%c' will be kept; you may remove them"
+			  "with '%s' will be kept; you may remove them"
 			  " yourself if you want to.\n"
 			  "An empty message aborts the commit.\n");
 		if (whence != FROM_COMMIT) {
@@ -945,12 +945,12 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 
 		fprintf(s->fp, "\n");
 		if (cleanup_mode == COMMIT_MSG_CLEANUP_ALL)
-			status_printf(s, GIT_COLOR_NORMAL, hint_cleanup_all, comment_line_char);
+			status_printf(s, GIT_COLOR_NORMAL, hint_cleanup_all, comment_line_str);
 		else if (cleanup_mode == COMMIT_MSG_CLEANUP_SCISSORS) {
 			if (whence == FROM_COMMIT && !merge_contains_scissors)
 				wt_status_add_cut_line(s->fp);
 		} else /* COMMIT_MSG_CLEANUP_SPACE, that is. */
-			status_printf(s, GIT_COLOR_NORMAL, hint_cleanup_space, comment_line_char);
+			status_printf(s, GIT_COLOR_NORMAL, hint_cleanup_space, comment_line_str);
 
 		/*
 		 * These should never fail because they come from our own