title: session_start fails with memcached handler
body: <p>i am trying to use memcached to store sessions but it seems session_start fails when trying to use the handler
  i used this simple script to see what is happening</p>
  
  <pre><code>ini_set('error_reporting', E_ALL);
  echo ini_get("session.save_handler").'&lt;br&gt;';
  echo ini_get('session.save_path').'&lt;br&gt;';
  echo(var_export(session_start(), true)).'&lt;br&gt;';
  ini_set("session.save_handler",'files');
  ini_set('session.save_path', '/tmp');
  echo ini_get("session.save_handler").'&lt;br&gt;';
  echo ini_get('session.save_path').'&lt;br&gt;';
  echo(var_export(session_start(), true));
  </code></pre>
  
  <p>which outputs this</p>
  
  <pre><code>memcached
  127.0.0.1:11211
  false
  files
  /tmp
  true
  </code></pre>
  
  <p>this is my configuration</p>
  
  <pre><code>memcache
  memcache support    enabled
  Active persistent connections   0
  Version 2.2.7
  Revision    $Revision: 327750 $
  Directive   Local Value Master Value
  memcache.allow_failover 1   1
  memcache.chunk_size 8192    8192
  memcache.default_port   11211   11211
  memcache.default_timeout_ms 1000    1000
  memcache.hash_function  crc32   crc32
  memcache.hash_strategy  standard    standard
  memcache.max_failover_attempts  20  20
  </code></pre>
  
  <p>these are my session settings</p>
  
  <pre><code>session
  Session Support enabled
  Registered save handlers    files user memcache sqlite
  Registered serializer handlers  php php_binary wddx
  Directive   Local Value Master Value
  session.auto_start  Off Off
  session.bug_compat_42   On  On
  session.bug_compat_warn On  On
  session.cache_expire    180 180
  session.cache_limiter   nocache nocache
  session.cookie_domain   xxxxxx.com  no value
  session.cookie_httponly Off Off
  session.cookie_lifetime 0   0
  session.cookie_path /   /
  session.cookie_secure   Off Off
  session.entropy_file    no value    no value
  session.entropy_length  0   0
  session.gc_divisor  100 100
  session.gc_maxlifetime  1440    1440
  session.gc_probability  1   1
  session.hash_bits_per_character 4   4
  session.hash_function   0   0
  session.name    CMSSESSID   PHPSESSID
  session.referer_check   no value    no value
  session.save_handler    memcached   memcached
  session.save_path   127.0.0.1:11211 127.0.0.1:11211
  session.serialize_handler   php php
  session.use_cookies On  On
  session.use_only_cookies    Off On
  session.use_trans_sid   0   0
  </code></pre>