simgear/props/props.*: added method to add exising SGPropertyNode_ptr as child.

Avoids the need to create a new child and copy recursively.

simgear/props/props.cxx

@@ -1098,6 +1098,20 @@ SGPropertyNode::addChild(const char * name, int min_index, bool append)
   return node;
 }
 
+SGPropertyNode_ptr SGPropertyNode::addChild(SGPropertyNode_ptr node, const std::string& name,
+        int min_index, bool append)
+{
+  int pos = append
+          ? std::max(find_last_child(name.c_str(), _children) + 1, min_index)
+          : first_unused_index(name.c_str(), _children, min_index);
+  node->_name = name;
+  node->_parent = this;
+  node->_index = pos;
+  _children.push_back(node);
+  fireChildAdded(node);
+  return node;
+}
+
 /**
  * Create multiple children with unused indices
  */

simgear/props/props.hxx

@@ -926,6 +926,16 @@ public:
                               bool append = true )
   { return addChild(name.c_str(), min_index, append); }
   
+  /**
+   * Add existing node as child.
+   *
+   * @param min_index Minimal index for new node (skips lower indices)
+   * @param append    Whether to simply use the index after the last used index
+   *                  or use a lower, unused index if it exists
+   */
+  SGPropertyNode_ptr addChild(SGPropertyNode_ptr node, const std::string& name,
+        int min_index=0, bool append=true);
+
   /**
    * Create multiple child nodes with the given name an unused indices
    *