allow time to first byte (of response headers)

to be logged by mod_logio.  

mod_logio was just a conveninent place to do this 
w/o writing a new filter or complicating an existing 
important one.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1671918 13f79535-47bb-0310-9956-ffa450edef68