RedCacheItem was using an union to reuse cache item memory
as a pipe item to release that specific cache item.
Instead of spreading that structure everywhere move the specific
optimization all in cache-item.tmpl.cpp.
This make also code less cluttered.
Add some comment on specific code.
Signed-off-by: Frediano Ziglio <freddy77@gmail.com>
Acked-by: Julien Ropé <jrope@gmail.com>
