mod_cache_socache: Fix a possible cached entity body corruption when it
is received from an origin server in multiple batches and forwarded by
mod_proxy.

Upstream buckets should be setaside when saving response body (store_body),
but since those will finally be flatten in the cache buffer (commit_entity),
let's save them directly into the buffer to avoid heap allocation(s) and
the final copy.

Reported by: Mike Pastore <mike oobak.org> 

Submitted by: ylavic
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1731082 13f79535-47bb-0310-9956-ffa450edef68