GPU1 retirement: Friday June 6 at 9am pacific time

As previously discussed, we are retiring GPU1.  We earlier discussed possibly doing this on June 2.  We've pushed this back a little, but will do so on Friday June 6 at 9am pacific time.  We'd like to take this opportunity to thank all the GPU1 donors who have pushed this technology very far, leading to the next generation GPU2 clients we have developed now.