Merge r1813991 from trunk:

Save a few bytes in the conf pool when handling 'ProxyHTMLDoctype' directive with a user defined  FPI


Submitted by: jailletc36
Reviewed by: jailletc36, niq, jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1820798 13f79535-47bb-0310-9956-ffa450edef68