Merge r3433: 

When we receive an If-Modified-Since on an ESI object, do not process the
conditional for the child object and pretend to send a 304 reply for them, if
we have decided to deliver the main object.

Fixes #386



git-svn-id: http://www.varnish-cache.org/svn/branches/2.0@3528 d4fa192b-c00b-0410-8231-f00ffab90ce4