io-threads on client-side in 2.0.0rc1

[Brent A Nelson <brent@xxxxxxxxxxxx>]

By the way, my dht over replicate setup is indeed still showing a 
performance boost with io-threads on the client, not just the server.

Both cp -a /usr (<6 minutes instead of >8) and dd (sometimes the same, 
sometimes >50MBps instead of <40MBps) tests come out significantly faster.

It was stated that io-threads should no longer matter on the client-side 
in 2.0, but that appears to be incorrect...

Thanks,

Brent