Description:
------------
When configured to use memcached for a session store, session_start returns true when the session lock key was already present (from a previous, long-running page request), and exhausts the retry attempts. An empty $_SESSION super global is created. When in the second page request (e.g. an AJAX call via xhr) finished and calls session_write_close() it then steps on the existing serialized data in memcached, corrupting the session state for the first, and still running page request.

The php-memcached code (php_memcached_session.c, line 85) returns a failure code to PHP session management, but it is being ignored.


Test script:
---------------
Can simulate by adding a key lock value to memcached (via telnet) before a call to session_start.

Expected result:
----------------
session_start to return false

Actual result:
--------------
session_start returns true