Another performance-related change to core_output_filter(): if we

Another performance-related change to core_output_filter(): if we
get a long stream of small buckets, so that multiple concatenation
steps are required in a single pass through the brigade, re-use the
buckets from the previous temp brigade when creating the next one.
This allows us to avoid making yet another copy of the previously
concatenated data.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@92197 13f79535-47bb-0310-9956-ffa450edef68