Added ProxySet directive (can be rename to something else).

The purpose is to be able to set the worker/balancer params
withouth the need for very long config lines :
<Proxy balancer://cluster>
  ProxySet stickysession=JSESSIONID
</Proxy>
Or...
ProxySet balancer://cluser nofaiover=On timeout=2


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@104794 13f79535-47bb-0310-9956-ffa450edef68