Merge r1389565, r1389566, r1389569:

    Allow for exposure of loadavg and server load via mod_headers

    Might as well show 'em all

    Document new mod_headers params: %l, %i, %b

Submitted by: jim
Reviewed by: jailletc36, druggeri, minfrin


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1418937 13f79535-47bb-0310-9956-ffa450edef68