Fix prefix issue when using PhpRedis

Hi Henrik,

Thanks for the last updates, it's very nice :)

I've got a weird error with PhpRedis. When PhpRedis is set up with an Redis::OPT_PREFIX, It does set the prefix to the key and to the timeout value. To set the resolved key in an array seems fixing this issue. @see: https://github.com/nicolasff/phpredis/issues/158

I made a gist with a reproductible example: https://gist.github.com/toin0u/5567583

My configuration:
* PHP 5.4.13
* Redis extention 2.2.2
* Redis 2.6.12
* Mac OS X 10.8.3

This PR "fixes" this problem. What do you think ?