rev-list --children

Just like --parents option shows the parents of commits, this shows the
children of commits.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/rev-list-options.txt

@@ -42,6 +42,10 @@ format, often found in E-mail messages.
 
 	Print the parents of the commit.
 
+--children::
+
+	Print the children of the commit.
+
 --timestamp::
 	Print the raw commit timestamp.
 

builtin-rev-list.c

@@ -36,6 +36,7 @@ static const char rev_list_usage[] =
 "    --reverse\n"
 "  formatting output:\n"
 "    --parents\n"
+"    --children\n"
 "    --objects | --objects-edge\n"
 "    --unpacked\n"
 "    --header | --pretty\n"
@@ -84,6 +85,15 @@ static void show_commit(struct commit *commit)
 			parents = parents->next;
 		}
 	}
+	if (revs.children.name) {
+		struct commit_list *children;
+
+		children = lookup_decoration(&revs.children, &commit->object);
+		while (children) {
+			printf(" %s", sha1_to_hex(children->item->object.sha1));
+			children = children->next;
+		}
+	}
 	show_decorations(commit);
 	if (revs.commit_format == CMIT_FMT_ONELINE)
 		putchar(' ');