Add the option to switch the serializer to igbinary in Redis cache store

Install phpredis with --enable-redis-igbinary like the one from Dotdep Install the PHP igbinary module. Go to Site administration -> Plugins -> Caching -> Configuration Select Redis store -> Edit Store If the phpredis module is compiled against igbinary the select box "Use serializer " should have two available options: "The default PHP serializer." "The igbinary serializer." Select "The igbinary serializer." Perform some exploratory testing, making redis the default application and session store. Then visiting pages, purging caches... changing redis instance key prefix, everything should continue working ok with the igbinary serializer in action. Note: Do a Redis database flush/restart (or change the prefix) before switching of serializer. This will be documented.