Add "rev-list" program that uses the new time-based commit listing.

This is probably what you'd want to see for "git log".

rev-list.c

@@ -0,0 +1,23 @@
+#include "cache.h"
+#include "commit.h"
+
+int main(int argc, char **argv)
+{
+	unsigned char sha1[20];
+	struct commit_list *list = NULL;
+	struct commit *commit;
+
+	if (argc != 2 || get_sha1_hex(argv[1], sha1))
+		usage("rev-list <commit-id>");
+
+	commit = lookup_commit(sha1);
+	if (!commit || parse_commit(commit) < 0)
+		die("bad commit object");
+
+	commit_list_insert(commit, &list);
+	do {
+		struct commit *commit = pop_most_recent_commit(&list);
+		printf("%s\n", sha1_to_hex(commit->object.sha1));
+	} while (list);
+	return 0;
+}