- Rename compatiblity mode to zend.ze2_compatibility_mode (it doesn't only affect auto-clone).

- Perform implementation checks even with simple inheritance (off when
  compatibility mode is enabled).
- Restore default arguments in interfaces and handle it correctly.
- Move registration of internal classes later in the startup sequence
  in order to have INI options available.

Zend/zend_variables.c

@@ -154,7 +154,7 @@ ZEND_API int _zval_copy_ctor(zval *zvalue ZEND_FILE_LINE_DC)
 			{
 				TSRMLS_FETCH();
 
-				if (EG(implicit_clone)) {
+				if (EG(ze1_compatibility_mode)) {
 					zvalue->value.obj = zvalue->value.obj.handlers->clone_obj(zvalue TSRMLS_CC);
 				} else {
 					Z_OBJ_HT_P(zvalue)->add_ref(zvalue TSRMLS_CC);