Fix %{DOCUMENT_URI} in SSI w/ default parser

  *) core: %{DOCUMENT_URI} used in nested SSI expressions should point to the
     URI originally requsted by the user, not the nested documents URI. This
     restores the behavior of this variable to match the "legacy" SSI parser.
     PR60624. 

Submitted By [Hank Ibell <hwibell gmail.com>]


Submitted by: covener
Reviewed by: covener, wrowe, ylavic


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1788448 13f79535-47bb-0310-9956-ffa450edef68