Rewrite resources when that moves them to a new domain

[GoogleCodeExporter]

Right now, we only move resources in accordance with 
ModPagespeedMapRewriteDomain if those resources change in some way (rewritte, 
cache-extended).  In order to benefit from shifting resources to cookieless 
domains, we should consider always rewriting resources that are subject to this 
directive.  The simplest way would be as follows:

1) Add logic to DomainLawyer etc. to detect when a resource url can be 
rewritten in this way.
2) Modify cache extension so that it also rewrites these resources.

Original issue reported on code.google.com by jmaes...@google.com on 3 Jan 2011 at 3:18