[librsvg] fix: implement rsvg_node_add_child()

[Federico Mena Quintero <federico src gnome org>]

commit 4853f512a67dbabfe3285d7e5a3cca51949b7003
Author: Federico Mena Quintero <federico gnome org>
Date:   Thu Feb 16 23:09:54 2017 -0600

    fix: implement rsvg_node_add_child()

 rust/src/node.rs |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)
---
diff --git a/rust/src/node.rs b/rust/src/node.rs
index 0eb18c0..df03e4c 100644
--- a/rust/src/node.rs
+++ b/rust/src/node.rs
@@ -255,8 +255,13 @@ pub extern fn rsvg_node_foreach_child (raw_node: *const RsvgNode, func: NodeFore
     assert! (!raw_node.is_null ());
     let node: &RsvgNode = unsafe { & *raw_node };
 
-    for child in node.children.borrow ().iter () {
-        let next = unsafe { func (child as *const RsvgNode, data) };
+    for child in &*node.children.borrow () {
+        let boxed_child = box_node (child.clone ());
+
+        let next = unsafe { func (boxed_child, data) };
+
+        unsafe { rsvg_node_unref (boxed_child); }
+
         if !next {
             break;
         }