Restore functionality broken by the mod_rewrite security fix:

rewrite map lookup keys and default values are now expanded
so that the lookup can depend on the requested URI etc.

Because the new code is recursive you can now write configurations
like the following (with nested map lookups) which wasn't directly
possible before -- you had to use a RewriteCond and a %N backref
instead, as in http://www.apache.org/docs/vhosts/mass.html#xtra-conf

RewriteMap tolower int:tolower
RewriteMap host2user txt:/home/www/conf/virtusertbl
RewriteRule /(.*) /home/${host2user:${tolower:%{HTTP_HOST}}|www}/public_html

PR: 6671


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86638 13f79535-47bb-0310-9956-ffa450edef68