take servers out of the mix based on rcode; add exponential backoff
take servers out of the mix based on rcode; add exponential backoff

Original author: Bob Halley <halley@dnspython.org>
Date: 2005-06-04 20:55:45

cluck/dnspython,leeclemens/dnspython,preo/dnspython,tomlanyon/dnspython,tow/dnspython,fjxhkj/dnspython,Abhayakara/dnspython,rcorrieri/dnspython