Fix a growing connection pool in core_output_filter() for

keepalive requests.  We were allocating a brigade out of the
connection pool; the number of these brigades allocated
per connection was theoretically unlimited.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@90736 13f79535-47bb-0310-9956-ffa450edef68