Get the length of a redis list and output it to graphite as a metric.

I use this to graph logstash queues as redis lists are the recommended queuing mechanism for logstash servers. You should be monitoring and graphing them to diagnose problems, this should help you measure your queues. :)
This code is pretty much copied from check redis length and redis graphite plugins, i deserve no credit.
fixed file extension for redis llen metric
removed random whitespace that failed tests
Merge pull request #321 from willejs/patch-1

Get the length of a redis list and output it to graphite as a metric.