Simpler, faster code for generating HTTP response headers:

Instead of passing a callback function to apr_table_do() to
generate one field at a time, just build an iovec containing
all the fields and make a single call to apr_brigade_writev().


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@97122 13f79535-47bb-0310-9956-ffa450edef68