Merge r1409437 from trunk:

Give the opportunity to the compiler to compute at compile time the strlen of the given
string. Most of the calls to ap_fputs are done with constant strings.
Submitted by: jailletc36
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1439393 13f79535-47bb-0310-9956-ffa450edef68