Add missing variables:
Introduced in r1132494
   CONTEXT_PREFIX
   CONTEXT_DOCUMENT_ROOT
and since the beginning of util_expr_eval.c  for
   HTTP_COOKIE

Description still missing.

+ synch layout with 2.4

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1595353 13f79535-47bb-0310-9956-ffa450edef68