If we accidentally specify AcceleratedHTTPCacheManager in a widely-called Script (Python) by mistake (that happened in reality), many responses will have wrong Cache-Control header and it is very hard to recover if they are cached in each browser's cache.
With this change, AcceleratedHTTPCacheManager is effective only when the object itself is directly published, so that we can prevent such unexpected cache pollution.
/cc @romain @jerome @vpelletier @tb