Support for GTX 4xx hardware

We have been working behind the scenes to optimize the Folding@home GPU client for the new NVIDIA GTX 4xx hardware.  So far, it's been going well with us hitting some strong performance numbers.  We are internally testing this and hope to soon (weeks) release this for outside beta testing.  Please note that GTX 4xx support will require a new client and also requires some changes to our cluster backend software.