mod_cache: Change the signature of the store_body() provider function

within the mod_cache provider interface to support an "in" brigade
and an "out" brigade instead of just a single input brigade. This
gives a cache provider the option to consume only part of the brigade
passed to it, rather than the whole brigade as was required before.
This fixes an out of memory and a request timeout condition that would
occur when the original document was a large file. Update the
mod_disk_cache provider implementation to take into account the new API.
Introduce CacheReadSize and CacheReadTime directives to mod_disk_cache
to control the amount of data to attempt to cache before sending the
data on to the client in the "out" brigade.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@996395 13f79535-47bb-0310-9956-ffa450edef68