Load: Re-add session.php.

`session.php` is occasionally included directly by custom external code, so should continue to be available. This behaviour is deprecated.

Partial revert of [38373].
See #36335, #39027.



git-svn-id: https://develop.svn.wordpress.org/trunk@39453 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/session.php

@@ -0,0 +1,11 @@
+<?php
+/**
+ * Session API
+ *
+ * @since 4.0.0
+ */
+
+_deprecated_file( basename( __FILE__ ), '4.7.0' );
+
+require_once( ABSPATH . WPINC . '/class-wp-session-tokens.php' );
+require_once( ABSPATH . WPINC . '/class-wp-user-meta-session-tokens.php' );