Proposal for improving performance/reliability of redis store with lots of simultaneous connections

Hi.  I made this patch that significantly improves the number of connections socket.io can handle with the redis store before falling over (on my machine, from about 3000 to about 8000).     My understanding of the internals isn't thorough enough to really know if this breaks anything, but from some quick tests with two servers and using the publish/subscribe mechanism it seems to be ok.  If you see any issues with it, let me know and I'll redo it.