Varnish/Apache issues

This reintroduces fixes for Varnish wordpress login/admin, fixes cookie issues from #84, and (hopefully) addresses the apache perf issue in #89 

With regard to apache performance, we're hardcoding a *minimum* `MaxClients` value of 5 which may cause lower end servers to use swap and thrash themselves a bit under heavy load. This is a tradeoff, since it may be better than limiting them to handling only 1 or 2 concurrent requests.