Simplified mod_env's directives to behave as most directives are
  expected, in that UnsetEnv will not unset a SetEnv and PassEnv
  directive following that UnsetEnv within the same container.
  Also provides a runtime startup warning if a PassEnv configured
  environment value is undefined.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@91611 13f79535-47bb-0310-9956-ffa450edef68