Test for slowlog

Hi, as discussed at the [issue#264][1].

Here is the pull request with a test for slowlog. The new parser seem to work well for slowlog.

For the old parser, i have a patch here [gist][2]. Those still on old parser can use this.

Nitesh

[1]:https://github.com/mranney/node_redis/issues/264
[2]:https://gist.github.com/3795279