Change the serialization semantics to:

* if a certain object is of class INCOMPLETE_CLASS, the serializer will
    lookup the previously stored original class name of that object, and
    use that class name to serialize the object.

Change the deserialization semantics to:

  * if the class of an object, which is to be instantiated, is not found
    in the current context, the class name will be stored for later
    retrieval, and the class of that object is changed to INCOMPLETE_CLASS.

All function calls, property gets, and property sets operating on an
object of class INCOMPLETE_CLASS cause the execution to halt and to
output an informative error message.

ext/standard/basic_functions.c

@@ -708,6 +708,7 @@ PHP_RINIT_FUNCTION(basic)
 	BG(locale_string) = NULL;
 	BG(user_compare_func_name) = NULL;
 	BG(array_walk_func_name) = NULL;
+	BG(incomplete_class) = NULL;
 	BG(page_uid) = -1;
 	BG(page_inode) = -1;
 	BG(page_mtime) = -1;