Fix the problem Sascha reported, about extension_dir

@- Fixed a bug that prevented a changed compile-time extension_dir from
@  affecting modules that were loaded via php.ini (Zeev)

ext/standard/dl.c

@@ -100,9 +100,9 @@ void php_dl(pval *file, int type, pval *return_value)
 
 
 	if (type==MODULE_PERSISTENT) {
-		/* Use the configuration hash directly */
+		/* Use the configuration hash directly, the INI mechanism is not yet initialized */
 		if (cfg_get_string("extension_dir", &extension_dir)==FAILURE) {
-			extension_dir = NULL;
+			extension_dir = PHP_EXTENSION_DIR;
 		}
 	} else {
 		extension_dir = PG(extension_dir);