merge r3137, r3198, r3199, r3353, r3370, r3371, r3398, r3399: cache related fixes: *) do not pass buf with empty cached response, this fixes "zero size buf in output" alert *) hide cacheable Set-Cookie and P3P FastCGI response headers *) test comma separator in "Cache-Control" *) a cache manager thread handle was overwritten by a cache loader thread handle, this caused an exit delay, the bug had been introduced in r3248 *) fix handling cached HTTP/0.9 response *) log proxied HTTP/0.9 responses status as "009" *) fix the "If-None-Match" header name *) fix a cached zero-length body case