rev-list.c example: use common utils, reorganize

examples/rev-list.c

-#include <stdio.h>
-#include <string.h>
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
 
-#include <git2.h>
+#include "common.h"
 
-static void check_error(int error_code, const char *action)
+static int revwalk_parseopts(git_repository *repo, git_revwalk *walk, int nopts, char **opts);
+
+int main (int argc, char **argv)
 {
-	if (!error_code)
-		return;
+	git_repository *repo;
+	git_revwalk *walk;
+	git_oid oid;
+	char buf[41];
+
+	git_threads_init();
 
-	const git_error *error = giterr_last();
-	fprintf(stderr, "Error %d %s: %s\n", -error_code, action,
-	        (error && error->message) ? error->message : "???");
-	exit(1);
+	check_lg2(git_repository_open_ext(&repo, ".", 0, NULL), "opening repository", NULL);
+	check_lg2(git_revwalk_new(&walk, repo), "allocating revwalk", NULL);
+	check_lg2(revwalk_parseopts(repo, walk, argc-1, argv+1), "parsing options", NULL);
+
+	while (!git_revwalk_next(&oid, walk)) {
+		git_oid_fmt(buf, &oid);
+		buf[40] = '\0';
+		printf("%s\n", buf);
+	}
+
+	git_threads_shutdown();
+	return 0;
 }
 
 static int push_commit(git_revwalk *walk, const git_oid *oid, int hide)
@@ -93,27 +111,3 @@ static int revwalk_parseopts(git_repository *repo, git_revwalk *walk, int nopts,
 	return 0;
 }
 
-int main (int argc, char **argv)
-{
-	int error;
-	git_repository *repo;
-	git_revwalk *walk;
-	git_oid oid;
-	char buf[41];
-
-	error = git_repository_open_ext(&repo, ".", 0, NULL);
-	check_error(error, "opening repository");
-
-	error = git_revwalk_new(&walk, repo);
-	check_error(error, "allocating revwalk");
-	error = revwalk_parseopts(repo, walk, argc-1, argv+1);
-	check_error(error, "parsing options");
-
-	while (!git_revwalk_next(&oid, walk)) {
-		git_oid_fmt(buf, &oid);
-		buf[40] = '\0';
-		printf("%s\n", buf);
-	}
-
-	return 0;
-}