better comments for _private fields removed a problem when copying an

* include/libxml/tree.h: better comments for _private fields
* tree.c: removed a problem when copying an entity reference.
Daniel
diff --git a/tree.c b/tree.c
index 14d5752..c55f4ff 100644
--- a/tree.c
+++ b/tree.c
@@ -2822,9 +2822,11 @@
 	} else {
             ret->children = node->children;
 	}
-    } else if (node->children != NULL)
+	ret->last = ret->children;
+    } else if (node->children != NULL) {
         ret->children = xmlStaticCopyNodeList(node->children, doc, ret);
-    UPDATE_LAST_CHILD_AND_PARENT(ret)
+	UPDATE_LAST_CHILD_AND_PARENT(ret)
+    }
     return(ret);
 }