Based on report from Ken Zalewski, on online doc.

Add missing Server-Variables useable in RewriteCond directive.
Introduced in r1132494
   CONTEXT_PREFIX
   CONTEXT_DOCUMENT_ROOT
Introduced in r737973
   IPV6
Missing for ages!
   SCRIPT_GROUP
   SCRIPT_USER

I have added where I found it logical, feel free to adjust.
I have also reordered this table to ease reading.
Finally, I have beautified some tables at the end.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1594088 13f79535-47bb-0310-9956-ffa450edef68