log: clarify comment about reflog cycles

When we're walking reflogs, we leave the commit buffer and
parents in place. A comment explains that this is due to
"cycles". But the interesting thing is the unsaid
implication: that the cycles (plus our clearing of the SEEN
flag) will cause us to show commits multiple times. Let's
spell it out.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/log.c

@@ -372,7 +372,10 @@ static int cmd_log_walk(struct rev_info *rev)
 			 */
 			rev->max_count++;
 		if (!rev->reflog_info) {
-			/* we allow cycles in reflog ancestry */
+			/*
+			 * We may show a given commit multiple times when
+			 * walking the reflogs.
+			 */
 			free_commit_buffer(commit);
 		}
 		free_commit_list(commit->parents);