surround %s with quotes when failed to lookup commit

The output may become confusing to recognize if the user
accidentally gave an extra opening space, like:

   $ git commit --fixup=" 6d6360b67e99c2fd82d64619c971fdede98ee74b"
   fatal: could not lookup commit  6d6360b67e99c2fd82d64619c971fdede98ee74b

and it will be better if we surround the %s specifier with single quotes.

Signed-off-by: Teng Long <dyroneteng@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/commit.c b/builtin/commit.c
index e67c4be..9ab57ea 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -763,7 +763,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 			struct commit *c;
 			c = lookup_commit_reference_by_name(squash_message);
 			if (!c)
-				die(_("could not lookup commit %s"), squash_message);
+				die(_("could not lookup commit '%s'"), squash_message);
 			ctx.output_encoding = get_commit_output_encoding();
 			repo_format_commit_message(the_repository, c,
 						   "squash! %s\n\n", &sb,
@@ -798,7 +798,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 		char *fmt;
 		commit = lookup_commit_reference_by_name(fixup_commit);
 		if (!commit)
-			die(_("could not lookup commit %s"), fixup_commit);
+			die(_("could not lookup commit '%s'"), fixup_commit);
 		ctx.output_encoding = get_commit_output_encoding();
 		fmt = xstrfmt("%s! %%s\n\n", fixup_prefix);
 		repo_format_commit_message(the_repository, commit, fmt, &sb,
@@ -1189,7 +1189,7 @@ static const char *read_commit_message(const char *name)
 
 	commit = lookup_commit_reference_by_name(name);
 	if (!commit)
-		die(_("could not lookup commit %s"), name);
+		die(_("could not lookup commit '%s'"), name);
 	out_enc = get_commit_output_encoding();
 	return repo_logmsg_reencode(the_repository, commit, NULL, out_enc);
 }